In this changelog, we document "large-ish" changes to Iris that affect even the
way the logic is used on paper. We also document changes in the Coq
development; every API-breaking change should be listed, but not every new
lemma.

## Iris master

**Changes in `algebra`**

* Define non-expansive instance for `dom`. This, in particular, makes it
possible to `iRewrite` below `dom` (even if the `dom` appears in `⌜ _ ⌝`).

**Changes in `bi`:**

* Rename `least_fixpoint_ind` into `least_fixpoint_iter`,
rename `greatest_fixpoint_coind` into `greatest_fixpoint_coiter`,
rename `least_fixpoint_strong_ind` into `least_fixpoint_ind`,
add lemmas `least_fixpoint_{ind_wf, ne', strong_mono}`, and
add lemmas `greatest_fixpoint_{coind, paco, ne', strong_mono}`.
* Move `persistently_forall_2` (`∀ <pers> ⊢ <pers> ∀`) out of the BI interface
into a new typeclass, `BiPersistentlyForall`. The BI interface instead just
demands the equivalent property for conjunction (`(<pers> P) ∧ (<pers> Q) ⊢
<pers> (P ∧ Q)`). This enables the IPM to support logics where the
persistently modality is defined with an existential quantifier. This also
necessitates removing `persistently_impl_plainly` from `BiPlainly` into a new
typeclass `BiPersistentlyImplPlainly`.
Proofs that are generic in `PROP` might have to add those new classes as
assumptions to remain compatible, and code that instantiates the BI interface
needs to provide instances for the new classes.

The following `sed` script helps adjust your code to the renaming (on macOS,
replace `sed` by `gsed`, installed via e.g. `brew install gnu-sed`).
Note that the script is not idempotent, do not run it twice.
```
sed -i -E -f- $(find theories -name "*.v") <<EOF
# least/greatest fixpoint renames
s/\bleast_fixpoint_ind\b/least_fixpoint_iter/g
s/\bgreatest_fixpoint_coind\b/greatest_fixpoint_coiter/g
s/\bleast_fixpoint_strong_ind\b/least_fixpoint_ind/g
EOF
```

## Iris 3.5.0 (2021-11-05)

The highlights and most notable changes of this release are:

* Coq 8.14 is now supported, while Coq 8.12 and Coq 8.13 remain supported.
* The proof mode now has native support for pure names `%H` in intro patterns,
without installing
[iris/string-ident](https://gitlab.mpi-sws.org/iris/string-ident). If you had
the plugin installed, to migrate simply uninstall the plugin and stop
importing it.
* The proof mode now supports destructing existentials with the `"[%x ...]"`
pattern.
* `iMod` and `iModIntro` now report an error message for mask mismatches.
* Performance improvements for the proof mode in `iFrame` in non-affine
logics, `iPoseProof`, and `iDestruct` (by Paolo G. Giarrusso, Bedrock Systems,
and Armaël Guéneau).
* The new `ghost_map` logic-level library supports a ghost `gmap K V` with an
authoritative view and per-element points-to facts written `k ↪[γ] w`.
* Weakest preconditions now support a flexible number of laters per
physical step of the operational semantics. See merge request
[!585](https://gitlab.mpi-sws.org/iris/iris/-/merge_requests/595) (by
Jacques-Henri Jourdan and Yusuke Matsushita).
* HeapLang now has an atomic `Xchg` (exchange) operation (by Simon Hudon,
Google).

This release was managed by Ralf Jung, Robbert Krebbers, and Tej Chajed, with
contributions from Amin Timany, Armaël Guéneau, Dan Frumin, Dmitry Khalanskiy,
Hoang-Hai Dang, Jacques-Henri Jourdan, Lennard Gäher, Michael Sammler, Paolo G.
Giarrusso, Ralf Jung, Robbert Krebbers, Simon Friis Vindum, Simon Hudon, Tej
Chajed, and Yusuke Matsushita. Thanks a lot to everyone involved!

**Changes in `algebra`:**

* Generalize the authorative elements of the `view`, `auth` and `gset_bij`
cameras to be parameterized by a [discardable fraction](iris/algebra/dfrac.v)
(`dfrac`) instead of a fraction (`frac`). Normal fractions are now denoted
`●{#q} a` and `●V{#q} a`. Lemmas affected by this have been renamed such that
the "frac" in their name has been changed into "dfrac". (by Simon Friis Vindum)
* Generalize `namespace_map` to `reservation_map` which enhances `gmap positive
A` with a notion of 'tokens' that enable allocating a particular name in the
map. See [algebra.reservation_map](iris/algebra/reservation_map.v) for further
information.
* Add `dyn_reservation_map` which further extends `reservation_map` with the
ability to dynamically allocate an infinite set of tokens. This is useful to
perform synchronized allocation of the same name in two maps/APIs without
dedicated support from one of the involved maps/APIs. See
[algebra.dyn_reservation_map](iris/algebra/dyn_reservation_map.v) for further
information.
* Demote the Camera structure on `list` to `iris_staging` since its composition
is not very well-behaved.
* Extend `gmap_view` with lemmas for "big" operations on maps.
* Typeclasses instances triggering a canonical structure search such as `Equiv`,
`Dist`, `Op`, `Valid`, `ValidN`, `Unit`, `PCore` now use an `Hint Extern`
based on `refine` instead of `apply`, in order to use Coq's newer unification
algorithm.
* Set `Hint Mode` for the classes `OfeDiscrete`, `Dist`, `Unit`, `CmraMorphism`,
`rFunctorContractive`, `urFunctorContractive`.
* Set `Hint Mode` for the stdpp class `Equiv`. This might require few spurious
type annotations until
[Coq bug #14441](https://github.com/coq/coq/issues/14441) is fixed.
* Add `max_prefix_list` RA on lists whose composition is only defined when one
operand is a prefix of the other. The result is the longer list.
* Add `NonExpansive` instances for `curry` and friends.

**Changes in `bi`:**

* Add new lemmas `big_sepM2_delete_l` and `big_sepM2_delete_r`.
* Rename `big_sepM2_lookup_1` → `big_sepM2_lookup_l` and
`big_sepM2_lookup_2` → `big_sepM2_lookup_r`.
* Add lemmas for swapping nested big-ops: `big_sep{L,M,S,MS}_sep{L,M,S,MS}`.
* Rename `big_sep{L,L2,M,M2,S}_intuitionistically_forall` →
`big_sep{L,L2,M,M2,S}_intro`, and `big_orL_lookup` → `big_orL_intro`.
* Rename `bupd_forall` to `bupd_plain_forall`, and add
`{bupd,fupd}_{and,or,forall,exist}`.
* Decouple `Wp` and `Twp` typeclasses from the `program_logic.language`
interface. The typeclasses are now parameterized over an expression and a
value type, instead of a language. This requires extra type annotations or
explicit coercions in a few cases, in particular `WP v {{ Φ }}` must now be
written `WP (of_val v) {{ Φ }}`.
* Improve `make_laterable`:
- Adjust definition such that `Laterable P` iff `P ⊢ make_laterable P`.
As a consequence, `make_laterable_elim` got weaker: elimination now requires
an except-0 modality (`make_laterable P -∗ ◇ P`).
- Add `iModIntro` support for `make_laterable`.
* Improvements to `BiMonoPred`:
- Use `□`/`-∗` instead of `<pers>`/`→`.
- Strengthen to ensure that functions for recursive calls are non-expansive.
* Add `big_andM` (big conjunction on finite maps) with lemmas similar to `big_andL`.
* Add transitive embedding that constructs an embedding of `PROP1` into `PROP3`
by combining the embeddings of `PROP1` into `PROP2` and `PROP2` into `PROP3`.
This construct is *not* declared as an instance to avoid TC search divergence.
(by Hai Dang, BedRock Systems)
* Improve notation printing around magic wands, view shifts, `WP`, Texan
triples, and logically atomic triples.
* Slight change to the `AACC` notation for atomic accessors (which is usually
only printed, not parsed): added a `,` before `ABORT`, for consistency with `COMM`.
* Add the lemmas `big_sepM_impl_strong` and `big_sepM_impl_dom_subseteq` that
generalize the existing `big_sepM_impl` lemma. (by Simon Friis Vindum)
* Add new instance `fractional_big_sepL2`. (by Paolo G. Giarrusso, BedRock Systems)

**Changes in `proofmode`:**

* Add support for pure names `%H` in intro patterns. This is now natively
supported whereas the previous experimental support required installing
https://gitlab.mpi-sws.org/iris/string-ident. (by Tej Chajed)
* Add support for destructing existentials with the intro pattern `[%x ...]`.
(by Tej Chajed)
* `iMod`/`iModIntro` show proper error messages when they fail due to mask
mismatches. To support this, the proofmode typeclass `FromModal` now takes an
additional pure precondition.
* Fix performance of `iFrame` in logics without `BiAffine`.
To adjust your code if you use such logics and define `Frame` instances,
ensure these instances to have priority at least 2: they should have either at
least 2 (non-dependent) premises, or an explicit priority.
References: docs for `frame_here_absorbing` in
[iris/proofmode/frame_instances.v](iris/proofmode/frame_instances.v) and
https://coq.inria.fr/refman/addendum/type-classes.html#coq:cmd.Instance. (by
Paolo G. Giarrusso, BedRock Systems)
* Rename the main entry point module for the proofmode from
`iris.proofmode.tactics` to `iris.proofmode.proofmode`. Under normal
circumstances, this should be the only proofmode file you need to import.
* Improve performance of the `iIntoEmpValid` tactic used by `iPoseProof`,
especially in the case of large goals and lemmas with many forall quantifiers.
(by Armaël Guéneau)
* Improve performance of the `iDestruct` tactic, by using user-provided names
more eagerly in order to avoid later calls to `iRename`.
(by Armaël Guéneau)

**Changes in `bi`:**

* Add lemmas characterizing big-ops over pure predicates (`big_sep*_pure*`).
* Move `BiAffine`, `BiPositive`, `BiLöb`, and `BiPureForall` from
`bi.derived_connectives` to `bi.extensions`.
* Strengthen `persistent_fractional` to support propositions that are persistent
and either affine or absorbing. (by Paolo G. Giarrusso, BedRock Systems)

**Changes in `base_logic`:**

* Add `ghost_map`, a logic-level library for a `gmap K V` with an authoritative
view and per-element points-to facts written `k ↪[γ] w`.
* Generalize the soundness lemma of the base logic `step_fupdN_soundness`.
It applies even if invariants stay open accross an arbitrary number of laters.
(by Jacques-Henri Jourdan)
* Rename those `*G` typeclasses that must be global singletons to `*GS`, and
their corresponding `preG` class to `GpreS`. Affects `invG`, `irisG`,
`gen_heapG`, `inv_heapG`, `proph_mapG`, `ownPG`, `heapG`.

**Changes in `program_logic`:**

* Change definition of weakest precondition to use a variable number of laters
(i.e., logical steps) for each physical step of the operational semantics,
depending on the number of physical steps executed since the begining of the
execution of the program. See merge request [!595](https://gitlab.mpi-sws.org/iris/iris/-/merge_requests/595).
This implies several API-breaking changes, which can be easily fixed in client
formalizations in a backward compatible manner as follows:
- Ignore the new parameter `ns` in the state interpretation, which
corresponds to a step counter.
- Use the constant function "0" for the new field `num_laters_per_step` of
`irisG`.
- Use `fupd_intro _ _` for the new field `state_interp_mono` of `irisG`.
- Some proofs using lifting lemmas and adequacy theorems need to be adapted
to ignore the new step counter.
(by Jacques-Henri Jourdan)
* Remove `wp_frame_wand_l`; add `wp_frame_wand` as more symmetric replacement.
* Swap the polarity of the mask in logically atomic triples, so that it matches
regular `WP` masks.
* Rename `iris_invG` to `iris_invGS`.

**Changes in `heap_lang`:**

* Rename `Build_loc` constructor for `loc` type to `Loc`.
* Add atomic `Xchg` ("exchange"/"swap") operation. (by Simon Hudon, Google LLC)

## Iris 3.4.0 (released 2021-02-16)

The highlights and most notable changes of this release are as follows:
* Coq 8.13 is now supported; the old Coq 8.9 and Coq 8.10 are not supported any
more.
* The new `view` RA construction generalizes `auth` to user-defined abstraction
relations. (thanks to Gregory Malecha for the inspiration)
* The new `dfrac` RA extends `frac` (fractions `0 < q ≤ 1`) with support for
"discarding" some part of the fraction in exchange for a persistent witness
that discarding has happened. This can be used to easily generalize fractional
permissions with support for persistently owning "any part" of the resource.
(by Simon Friis Vindum)
* The new `gmap_view` RA provides convenient lemmas for ghost ownership
of heap-like structures with an "authoritative" view. Thanks to `dfrac`, it
supports both exclusive (mutable) and persistent (immutable) ownership of
individual map elements.
* With this release we are beginning to provide logic-level abstractions for
ghost state, which have the advantage that the user does not have to directly
interact with RAs to use them.
- `ghost_var` provides a logic-level abstraction of ghost variables: a mutable
"variable" with fractional ownership.
- `mono_nat` provides a "monotone counter" with a persistent witnesses
representing a lower bound of the current counter value. (by Tej Chajed)
- `gset_bij` provides a monotonically growing partial bijection; this is
useful in particular when building binary logical relations for languages
with a heap.
* HeapLang provides a persistent read-only points-to assertion `l ↦□ v`.
(by Simon Friis Vindum)
* We split Iris into multiple opam packages: `coq-iris` no longer contains
HeapLang, which is now in a separate package `coq-iris-heap-lang`. The two
packages `coq-iris-deprecated` (for old modules that we eventually plan to
remove entirely) and `coq-iris-staging` (for new modules that are not yet
ready for prime time) exist only as development versions, so they are not part
of this release.
* The proofmode now does a better job at picking reasonable names when moving
variables into the Coq context without a name being explicitly given by the
user. However, the exact variable names remain unspecified. (by Tej Chajed)

Further details are given in the changelog below.

This release of Iris was managed by Ralf Jung and Robbert Krebbers, with
contributions by Arthur Azevedo de Amorim, Dan Frumin, Enrico Tassi, Hai Dang,
Michael Sammler, Paolo G. Giarrusso, Rodolphe Lepigre, Simon Friis Vindum, Tej
Chajed, and Yusuke Matsushita. Thanks a lot to everyone involved!

**Changes in `algebra`:**

* Add constructions to define a camera through restriction of the validity predicate
(`iso_cmra_mixin_restrict`) and through an isomorphism (`iso_cmra_mixin`).
* Add a `frac_agree` library which encapsulates `frac * agree A` for some OFE
`A`, and provides some useful lemmas.
* Add the view camera `view`, which generalizes the authoritative camera
`auth` by being parameterized by a relation that relates the authoritative
element with the fragments.
* Add the camera of discardable fractions `dfrac`. This is a generalization of
the normal fractional camera.
See [algebra.dfrac](iris/algebra/dfrac.v) for further information.
* Add `gmap_view`, a camera providing a "view of a `gmap`". The authoritative
element is any `gmap`; the fragment provides fractional ownership of a single
key, including support for persistent read-only ownership through `dfrac`.
See [algebra.lib.gmap_view](iris/algebra/lib/gmap_view.v) for further information.
* Add `mono_nat`, a wrapper for `auth max_nat`. The result is an authoritative
`nat` where a fragment is a lower bound whose ownership is persistent.
See [algebra.lib.mono_nat](iris/algebra/lib/mono_nat.v) for further information.
* Add the `gset_bij` resource algebra for monotone partial bijections.
See [algebra.lib.gset_bij](iris/algebra/lib/gset_bij.v) for further information.
* Rename `agree_op_inv'` → `to_agree_op_inv`,
`agree_op_invL'` → `to_agree_op_inv_L`, and add `to_agree_op_invN`.
* Rename `auth_auth_frac_op_invL` → `auth_auth_frac_op_inv_L`,
`excl_auth_agreeL` → `excl_auth_agree_L`,
`frac_auth_agreeL` → `frac_auth_agree_L`, and
`ufrac_auth_agreeL` → `ufrac_auth_agree_L`.
* Fix direction of `auth_auth_validN` to make it consistent with similar lemmas,
e.g., `auth_auth_valid`. The direction is now `✓{n} (● a) ↔ ✓{n} a`.
* Rename `auth_both_valid` to `auth_both_valid_discrete` and
`auth_both_frac_valid` to `auth_both_frac_valid_discrete`. The old name is
used for new, stronger lemmas that do not assume discreteness.
* Redefine the authoritative camera in terms of the view camera. As part of this
change, we have removed lemmas that leaked implementation details. Hence, the
only way to construct elements of `auth` is via the elements `●{q} a` and
`◯ b`. The constructor `Auth`, and the projections `auth_auth_proj` and
`auth_frag_proj` no longer exist. Lemmas that referred to these constructors
have been removed, in particular: `auth_equivI`, `auth_validI`,
`auth_included`, `auth_valid_discrete`, and `auth_both_op`. For validity, use
`auth_auth_valid*`, `auth_frag_valid*`, or `auth_both_valid*` instead.
* Rename `auth_update_core_id` into `auth_update_frac_alloc`.
* Rename `cmra_monotone_valid` into `cmra_morphism_valid` (this rename was
forgotten in !56).
* Move the `*_validI` and `*_equivI` lemmas to a new module, `base_logic.algebra`.
That module is exported by `base_logic.base_logic` so it should usually be
available everywhere without further changes.
* The authoritative fragment `✓ (◯ b : auth A)` is no longer definitionally
equal to `✓ b`.
* Change `*_valid` lemma statements involving fractions to use `Qp` addition and
inequality instead of RA composition and validity (also in `base_logic` and
the higher layers).
* Move `algebra.base` module to `prelude.prelude`.
* Strengthen `cmra_op_discrete` to assume only `✓{0} (x1 ⋅ x2)` instead of `✓
(x1 ⋅ x2)`.
* Rename the types `ofeT`→`ofe`, `cmraT`→`cmra`, `ucmraT`→`ucmra`, and the
constructors `OfeT`→`Ofe`, `CmraT`→`Cmra`, and `UcmraT`→`Ucmra` since the `T`
suffix is not needed. This change makes these names consistent with `bi`,
which also does not have a `T` suffix.
* Rename typeclass instances of CMRA operational typeclasses (`Op`, `Core`,
`PCore`, `Valid`, `ValidN`, `Unit`) to have a `_instance` suffix, so that
their original names are available to use as lemma names.
* Rename `frac_valid'`→`frac_valid`, `frac_op'`→`frac_op`,
`ufrac_op'`→`ufrac_op`, `coPset_op_union` → `coPset_op`, `coPset_core_self` →
`coPset_core`, `gset_op_union` → `gset_op`, `gset_core_self` → `gset_core`,
`gmultiset_op_disj_union` → `gmultiset_op`, `gmultiset_core_empty` →
`gmultiset_core`, `nat_op_plus` → `nat_op`, `max_nat_op_max` →
`max_nat_op`. Those names were previously blocked by typeclass instances.

**Changes in `bi`:**

* Add big op lemmas `big_op{L,L2,M,M2,S}_intuitionistically_forall` and
`big_sepL2_forall`, `big_sepMS_forall`, `big_sepMS_impl`, and `big_sepMS_dup`.
* Add lemmas to big-ops that provide ownership of a single element and permit
changing the quantified-over predicate when re-assembling the big-op:
`big_sepL_lookup_acc_impl`, `big_sepL2_lookup_acc_impl`,
`big_sepM_lookup_acc_impl`, `big_sepM2_lookup_acc_impl`,
`big_sepS_elem_of_acc_impl`, `big_sepMS_elem_of_acc_impl`.
* Add lemmas `big_sepM_filter'` and `big_sepM_filter` matching the corresponding
`big_sepS` lemmas.
* Add lemmas for big-ops of magic wands: `big_sepL_wand`, `big_sepL2_wand`,
`big_sepM_wand`, `big_sepM2_wand`, `big_sepS_wand`, `big_sepMS_wand`.
* Add notation `¬ P` for `P → False` to `bi_scope`.
* Add `fupd_mask_intro` which can be conveniently `iApply`ed to goals of the
form `|={E1,E2}=>` to get rid of the `fupd` in the goal if `E2 ⊆ E1`. The
lemma `fupd_mask_weaken Enew` can be `iApply`ed to shrink the first mask to
`Enew` without getting rid of the modality; the same effect can also be
obtained slightly more conveniently by using `iMod` with `fupd_mask_subseteq
Enew`. To make the new names work, rename some existing lemmas:
`fupd_intro_mask` → `fupd_mask_intro_subseteq`,
`fupd_intro_mask'` → `fupd_mask_subseteq` (implicit arguments also changed
here), `fupd_mask_weaken` → `fupd_mask_intro_discard`. Remove `fupd_mask_same`
since it was unused and obscure. In the `BiFUpd` axiomatization, rename
`bi_fupd_mixin_fupd_intro_mask` to `bi_fupd_mixin_fupd_mask_subseteq` and
weaken the lemma to be specifically about `emp` (the stronger version can be
derived).
* Remove `bi.tactics` with tactics that predate the proofmode (and that have not
been working properly for quite some time).
* Strengthen `persistent_sep_dup` to support propositions that are persistent
and either affine or absorbing.
* Fix the statement of the lemma `fupd_plainly_laterN`; the old lemma was a
duplicate of `fupd_plain_laterN`.
* Strengthen `big_sepL2_app_inv` by weakening a premise (it is sufficient for
one of the two pairs of lists to have equal length).
* Rename `equiv_entails` → `equiv_entails_1_1`,
`equiv_entails_sym` → `equiv_entails_1_2`, and `equiv_spec` → `equiv_entails`.
* Remove the laws `pure_forall_2 : (∀ a, ⌜ φ a ⌝) ⊢ ⌜ ∀ a, φ a ⌝` from the BI
interface and factor it into a type class `BiPureForall`.

**Changes in `proofmode`:**

* The proofmode now preserves user-supplied names for existentials when using
`iDestruct ... as (?) "..."`. This is backwards-incompatible if you were
relying on the previous automatic names (which were always "H", possibly
freshened). It also requires some changes if you were implementing `IntoExist`
yourself, since the typeclass now forwards names. If your instance transforms
one `IntoExist` into another, you can generally just forward the name from the
premise.
* The proofmode also preserves user-supplied names in `iIntros`, for example
with `iIntros (?)` and `iIntros "%"`, as described for destructing
existentials above. As part of this change, it now uses a base name of `H` for
pure facts rather than the previous default of `a`. This also requires some
changes if you were implementing `FromForall`, in order to forward names.
* Make `iFrame` "less" smart w.r.t. clean up of modalities. It now consistently
removes the modalities `<affine>`, `<absorbing>`, `<persistent>` and `□` only
if the result after framing is `True` or `emp`. In particular, it no longer
removes `<affine>` if the result after framing is affine, and it no longer
removes `□` if the result after framing is intuitionistic.
* Allow framing below an `<affine>` modality if the hypothesis that is framed is
affine. (Previously, framing below `<affine>` was only possible if the
hypothesis that is framed resides in the intuitionistic context.)
* Add Coq side-condition `φ` to class `ElimAcc` (similar to what we already had
for `ElimInv` and `ElimModal`).
* Add a tactic `iSelect pat tac` (similar to `select` in std++) which runs the
tactic `tac H` with the name `H` of the last hypothesis of the intuitionistic
or spatial context matching `pat`. The tactic `iSelect` is used to implement:
+ `iRename select (pat)%I into name` which renames the matching hypothesis,
+ `iDestruct select (pat)%I as ...` which destructs the matching hypothesis,
+ `iClear select (pat)%I` which clears the matching hypothesis,
+ `iRevert select (pat)%I` which reverts the matching hypothesis,
+ `iFrame select (pat)%I` which cancels the matching hypothesis.

**Changes in `base_logic`:**

* Add a `ghost_var` library that provides (fractional) ownership of a ghost
variable of arbitrary `Type`.
* Define a ghost state library on top of the `mono_nat` resource algebra.
See [base_logic.lib.mono_nat](iris/base_logic/lib/mono_nat.v) for further
information.
* Define a ghost state library on top of the `gset_bij` resource algebra.
See [base_logic.lib.gset_bij](iris/base_logic/lib/gset_bij.v) for further
information.
* Extend the `gen_heap` library with read-only points-to assertions using
[discardable fractions](iris/algebra/dfrac.v).
+ The `mapsto` connective now takes a `dfrac` rather than a `frac` (i.e.,
positive rational number `Qp`).
+ The notation `l ↦{ dq } v` is generalized to discardable fractions
`dq : dfrac`.
+ The new notation `l ↦{# q} v` is used for a concrete fraction `q : frac`
(e.g., to enable writing `l ↦{# 1/2} v`).
+ The new notation `l ↦□ v` is used for the discarded fraction. This
persistent proposition provides read-only access to `l`.
+ The lemma `mapsto_persist : l ↦{dq} v ==∗ l ↦□ v` is used for making the
location `l` read-only.
+ See the [changes to HeapLang](https://gitlab.mpi-sws.org/iris/iris/-/merge_requests/554)
for an indication on how to adapt your language.
+ See the [changes to iris-examples](https://gitlab.mpi-sws.org/iris/examples/-/commit/a8425b708ec51d918d5cf6eb3ab6fde88f4e2c2a)
for an indication on how to adapt your development. In particular, instead
of `∃ q, l ↦{q} v` you likely want to use `l ↦□ v`, which has the advantage
of being persistent (rather than just duplicable).
* Change type of some ghost state lemmas (mostly about allocation) to use `∗`
instead of `∧` (consistent with our usual style). This affects the following
lemmas: `own_alloc_strong_dep`, `own_alloc_cofinite_dep`, `own_alloc_strong`,
`own_alloc_cofinite`, `own_updateP`, `saved_anything_alloc_strong`,
`saved_anything_alloc_cofinite`, `saved_prop_alloc_strong`,
`saved_prop_alloc_cofinite`, `saved_pred_alloc_strong`,
`saved_pred_alloc_cofinite`, `auth_alloc_strong`, `auth_alloc_cofinite`,
`auth_alloc`.
* Change `uPred_mono` to only require inclusion at the smaller step-index.
* Put `iProp`/`iPreProp`-isomorphism into the `own` construction. This affects
clients that define higher-order ghost state constructions. Concretely, when
defining an `inG`, the functor no longer needs to be applied to `iPreProp`,
but should be applied to `iProp`. This avoids clients from having to push
through the `iProp`/`iPreProp`-isomorphism themselves, which is now handled
once and for all by the `own` construction.
* Rename `gen_heap_ctx` to `gen_heap_interp`, since it is meant to be used in
the state interpretation of WP and since `_ctx` is elsewhere used as a suffix
indicating "this is a persistent assumption that clients should always have in
their context". Likewise, rename `proph_map_ctx` to `proph_map_interp`.
* Move `uPred.prod_validI`, `uPred.option_validI`, and
`uPred.discrete_fun_validI` to the new `base_logic.algebra` module. That
module is exported by `base_logic.base_logic` so these names are now usually
available everywhere, and no longer inside the `uPred` module.
* Remove the `gen_heap` notations `l ↦ -` and `l ↦{q} -`. They were barely used
and looked very confusing in context: `l ↦ - ∗ P` looks like a magic wand.
* Change `gen_inv_heap` notation `l ↦□ I` to `l ↦_I □`, so that `↦□` can be used
by `gen_heap`.
* Strengthen `mapsto_valid_2` conclusion from `✓ (q1 + q2)%Qp` to
`⌜✓ (q1 + q2)%Qp ∧ v1 = v2⌝`.
* Change `gen_heap_init` to also return ownership of the points-to facts for the
initial heap.
* Rename `mapsto_mapsto_ne` to `mapsto_frac_ne`, and add a simpler
`mapsto_ne` that does not require reasoning about fractions.
* Deprecate the `auth` and `sts` modules. These were logic-level wrappers around
the underlying RAs; as far as we know, they are unused since they were not
flexible enough for practical use.
* Deprecate the `viewshift` module, which defined a binary view-shift connective
with an implicit persistence modality. It was unused and too easily confused
with `={_}=∗`, the binary view-shift (fancy update) *without* a persistence
modality.

**Changes in `program_logic`:**

* `wp_strong_adequacy` now applies to an initial state with multiple
threads instead of only a single thread. The derived adequacy lemmas
are unchanged.
* `pure_exec_fill` is no longer registered as an instance for `PureExec`, to
avoid TC search attempting to apply this instance all the time.
* Merge `wp_value_inv`/`wp_value_inv'` into `wp_value_fupd`/`wp_value_fupd'` by
making the lemmas bidirectional.
* Generalize HeapLang's `mapsto` (`↦`), `array` (`↦∗`), and atomic heap
connectives to discardable fractions. See the CHANGELOG entry in the category
`base_logic` for more information.
* Opening an invariant or eliminating a mask-changing update modality around a
non-atomic weakest precondition creates a side-condition `Atomic ...`.
Before, this would fail with the unspecific error "iMod: cannot eliminate
modality (|={E1,E2}=> ...) in (WP ...)".
* In `Ectx_step` and `step_atomic`, mark the parameters that are determined by
the goal as implicit.
* Deprecate the `hoare` module to prevent accidental usage; the recommended way
to write Hoare-style specifications is to use Texan triples.

**Changes in `heap_lang`:**

* `wp_pures` now turns goals of the form `WP v {{ Φ }}` into `Φ v`.
* Fix `wp_bind` in case of a NOP (i.e., when the given expression pattern is
already at the top level).
* The `wp_` tactics now preserve the possibility of doing a fancy update when
the expression reduces to a value.
* Move `IntoVal`, `AsVal`, `Atomic`, `AsRecV`, and `PureExec` instances to their
own file [heap_lang.class_instances](iris_heap_lang/class_instances.v).
* Move `inv_head_step` tactic and `head_step` auto hints (now part of new hint
database `head_step`) to [heap_lang.tactics](iris_heap_lang/tactics.v).
* The tactic `wp_apply` no longer performs `wp_pures` before applying the given
lemma. The new tactic `wp_smart_apply` repeatedly performs single `wp_pure`
steps until the lemma matches the goal.

The following `sed` script helps adjust your code to the renaming (on macOS,
replace `sed` by `gsed`, installed via e.g. `brew install gnu-sed`).
Note that the script is not idempotent, do not run it twice.
```
sed -i -E -f- $(find theories -name "*.v") <<EOF
# agree and L suffix renames
s/\bagree_op_inv'/to_agree_op_inv/g
s/\bagree_op_invL'/to_agree_op_inv_L/g
s/\bauth_auth_frac_op_invL\b/auth_auth_frac_op_inv_L/g
s/\b(excl|frac|ufrac)_auth_agreeL/\1_auth_agree_L/g
# auth_both_valid
s/\bauth_both_valid\b/auth_both_valid_discrete/g
s/\bauth_both_frac_valid\b/auth_both_frac_valid_discrete/g
# gen_heap_ctx and proph_map_ctx
s/\bgen_heap_ctx\b/gen_heap_interp/g
s/\bproph_map_ctx\b/proph_map_interp/g
# other gen_heap changes
s/\bmapsto_mapsto_ne\b/mapsto_frac_ne/g
# remove Ts in algebra
s/\bofeT\b/ofe/g
s/\bOfeT\b/Ofe/g
s/\bcmraT\b/cmra/g
s/\bCmraT\b/Cmra/g
s/\bucmraT\b/ucmra/g
s/\bUcmraT\b/Ucmra/g
# _op/valid/core lemmas
s/\b(u?frac_(op|valid))'/\1/g
s/\b((coPset|gset)_op)_union\b/\1/g
s/\b((coPset|gset)_core)_self\b/\1/g
s/\b(gmultiset_op)_disj_union\b/\1/g
s/\b(gmultiset_core)_empty\b/\1/g
s/\b(nat_op)_plus\b/\1/g
s/\b(max_nat_op)_max\b/\1/g
# equiv_spec
s/\bequiv_entails\b/equiv_entails_1_1/g
s/\bequiv_entails_sym\b/equiv_entails_1_2/g
s/\bequiv_spec\b/equiv_entails/g
EOF
```

## Iris 3.3.0 (released 2020-07-15)

This release does not have any outstanding highlights, but contains a large
number of improvements all over the board. For instance:

* `heap_lang` now supports deallocation as well as better reasoning about
"invariant locations" (locations that perpetually satisfy some Coq-level
invariant).
* Invariants (`inv N P`) are more flexible, now also supporting splitting
and merging of invariants with respect to separating conjunction.
* Performance of the proofmode for BIs constructed on top of other BIs (e.g.,
`monPred`) was greatly improved, leading to up to 70% speedup in individual
files. As part of this refactoring, the proofmode can now also be instantiated
with entirely "logical" notion of BIs that do not have a (non-trivial) metric
structure, and still support reasoning about ▷.
* The proof mode now provides experimental support for naming pure facts in
intro patterns. See
[iris/string-ident](https://gitlab.mpi-sws.org/iris/string-ident) for details.
* Iris now provides official ASCII notation. We still recommend using the
Unicode notation for better consistency and interoperability with other Iris
libraries, but provide ASCII notation for when Unicode is not an option.
* We removed several coercions, fixing "ambiguous coercion path" warnings and
solving some readability issues.
* Coq 8.10, 8.11, and 8.12 are newly supported by this release, and Coq 8.7 and
8.8 are no longer supported.

Further details are given in the changelog below. We always first list the
potentially breaking changes, then (some of) the additions.

This release of Iris received contributions by Abel Nieto, Amin Timany, Dan
Frumin, Derek Dreyer, Dmitry Khalanskiy, Gregory Malecha, Jacques-Henri Jourdan,
Jonas Kastberg, Jules Jacobs, Matthieu Sozeau, Maxime Dénès, Michael Sammler,
Paolo G. Giarrusso, Ralf Jung, Robbert Krebbers, Simon Friis Vindum, Simon
Spies, and Tej Chajed. Thanks a lot to everyone involved!

**Changes in `heap_lang`:**

* Remove global `Open Scope Z_scope` from `heap_lang.lang`, and leave it up to
reverse dependencies if they want to `Open Scope Z_scope` or not.
* Fix all binary operators performing pointer arithmetic (instead of just the
dedicated `OffsetOp` operator doing that).
* Rename `heap_lang.lifting` to `heap_lang.primitive_laws`. There now also
exists `heap_lang.derived_laws`.
* Make lemma names for `fill` more consistent
- Use the `_inv` suffix for the the backwards directions:
`reducible_fill` → `reducible_fill_inv`,
`reducible_no_obs_fill` → `reducible_no_obs_fill_inv`,
`not_stuck_fill` → `not_stuck_fill_inv`.
- Use the non-`_inv` names (that freed up) for the forwards directions:
`reducible_fill`, `reducible_no_obs_fill`, `irreducible_fill_inv`.
* Remove namespace `N` from `is_lock`.

* Add support for deallocation of locations via the `Free` operation.
* Add a fraction to the heap_lang `array` assertion.
* Add `lib.array` module for deallocating, copying and cloning arrays.
* Add TWP (total weakest-pre) lemmas for arrays.
* Add a library for "invariant locations": heap locations that will not be
deallocated (i.e., they are GC-managed) and satisfy some pure, Coq-level
invariant. See `iris.base_logic.lib.gen_inv_heap` for details.
* Add the ghost state for "invariant locations" to `heapG`. This affects the
statement of `heap_adequacy`, which is now responsible for initializing the
"invariant locations" invariant.
* Add lemma `mapsto_mapsto_ne : ¬ ✓(q1 + q2)%Qp → l1 ↦{q1} v1 -∗ l2 ↦{q2} v2 -∗ ⌜l1 ≠ l2⌝`.
* Add lemma `is_lock_iff` and show that `is_lock` is contractive.

**Changes in `program_logic`:**

* In the axiomatization of ectx languages, replace the axiom of positivity of
context composition with an axiom that says if `fill K e` takes a head step,
then either `K` is the empty evaluation context or `e` is a value.

**Changes in the logic (`base_logic`, `bi`):**

* Rename some accessor-style lemmas to consistently use the suffix `_acc`
instead of `_open`:
`inv_open` → `inv_acc`, `inv_open_strong` → `inv_acc_strong`,
`inv_open_timeless` → `inv_acc_timeless`, `na_inv_open` → `na_inv_acc`,
`cinv_open` → `cinv_acc`, `cinv_open_strong` → `cinv_acc_strong`,
`auth_open` → `auth_acc`, `sts_open` → `sts_acc`.
To make this work, also rename `inv_acc` → `inv_alter`.
(Most developments should be unaffected as the typical way to invoke these
lemmas is through `iInv`, and that does not change.)
* Change `inv_iff`, `cinv_iff` and `na_inv_iff` to make order of arguments
consistent and more convenient for `iApply`. They are now of the form
`inv N P -∗ ▷ □ (P ↔ Q) -∗ inv N Q` and (similar for `na_inv_iff` and
`cinv_iff`), following e.g., `inv_alter` and `wp_wand`.
* Rename `inv_sep_1` → `inv_split_1`, `inv_sep_2` → `inv_split_2`, and
`inv_sep` → `inv_split` to be consistent with the naming convention in boxes.
* Update the strong variant of the accessor lemma for cancellable invariants to
match that of regular invariants, where you can pick the mask at a later time.
(The other part that makes it strong is that you get back the token for the
invariant immediately, not just when the invariant is closed again.)
* Rename `iProp`/`iPreProp` to `iPropO`/`iPrePropO` since they are `ofeT`s.
Introduce `iProp` for the `Type` carrier of `iPropO`.
* Flatten the BI hierarchy by merging the `bi` and `sbi` canonical structures.
This gives significant performance benefits on developments that construct BIs
from BIs (e.g., use `monPred`). For, example it gives a performance gain of 37%
overall on lambdarust-weak, with improvements for individual files up to 72%,
see Iris issue #303. The concrete changes are as follows:
+ The `sbi` canonical structure has been removed.
+ The `bi` canonical structure contains the later modality. It does not
require the later modality to be contractive or to satisfy the Löb rule, so
we provide a smart constructor `bi_later_mixin_id` to get the later axioms
"for free" if later is defined to be the identity function.
+ There is a separate class `BiLöb`, and a "free" instance of that class if
the later modality is contractive. A `BiLöb` instance is required for the
`iLöb` tactic, and for timeless instances of implication and wand.
+ There is a separate type class `BiInternalEq` for BIs with a notion of
internal equality (internal equality was part of `sbi`). An instance of this
class is needed for the `iRewrite` tactic, and the various lemmas about
internal equality.
+ The class `SbiEmbed` has been removed and been replaced by classes
`BiEmbedLater` and `BiEmbedInternalEq`.
+ The class `BiPlainly` has been generalized to BIs without internal equality.
As a consequence, there is a separate class `BiPropExt` for BIs with
propositional extensionality (i.e., `■ (P ∗-∗ Q) ⊢ P ≡ Q`).
+ The class `BiEmbedPlainly` is a bi-entailment (i.e., `⎡■ P⎤ ⊣⊢ ■ ⎡P⎤`
instead of `■ ⎡P⎤ ⊢ ⎡■ P⎤`) as it has been generalized to BIs without a
internal equality. In the past, the left-to-right direction was obtained for
"free" using the rules of internal equality.
* Remove coercion from `iProp` (and other MoSeL propositions) to `Prop`.
Instead, use the new unary notation `⊢ P`, or `⊢@{PROP} P` if the proposition
type cannot be inferred. This also means that `%I` should not be necessary any
more when stating lemmas, as `P` above is automatically parsed in scope `%I`.
* Some improvements to the `bi/lib/core` construction:
+ Rename `coreP_wand` into `coreP_entails` since it does not involve wands.
+ Generalize `coreP_entails` to non-affine BIs, and prove more convenient
version `coreP_entails'` for `coreP P` with `P` affine.
+ Add instance `coreP_affine P : Affine P → Affine (coreP P)` and
lemma `coreP_wand P Q : <affine> ■ (P -∗ Q) -∗ coreP P -∗ coreP Q`.
* Remove notation for 3-mask step-taking updates, and made 2-mask notation less
confusing by distinguishing it better from mask-changing updates.
Old: `|={Eo,Ei}▷=> P`. New: `|={Eo}[Ei]▷=> P`.
Here, `Eo` is the "outer mask" (used at the beginning and end) and `Ei` the
"inner mask" (used around the ▷ in the middle).
As part of this, the lemmas about the 3-mask variant were changed to be about
the 2-mask variant instead, and `step_fupd_mask_mono` now also has a more
consistent argument order for its masks.

* Add a counterexample showing that sufficiently powerful cancellable invariants
with a linear token subvert the linearity guarantee (see
`bi.lib.counterexmples` for details).
* Redefine invariants as "semantic invariants" so that they support
splitting and other forms of weakening.
* Add lemmas `inv_combine` and `inv_combine_dup_l` for combining invariants.
* Add the type `siProp` of "plain" step-indexed propositions, together with
basic proofmode support.
* New ASCII versions of Iris notations. These are marked parsing only and
can be made available using `Require Import iris.bi.ascii`. The new
notations are (notations marked [†] are disambiguated using notation scopes):
- entailment: `|-` for `⊢` and `-|-` for `⊣⊢`
- logic[†]: `->` for `→`, `/\\` for `∧`, `\\/` for `∨`, and `<->` for `↔`
- quantifiers[†]: `forall` for `∀` and `exists` for `∃`
- separation logic: `**` for `∗`, `-*` for `-∗`, and `*-*` for `∗-∗`
- step indexing: `|>` for `▷`
- modalities: `<#>` for `□` and `<except_0>` for `◇`
- most derived notations can be computed from previous notations using the
substitutions above, e.g. replace `∗` with `*` and `▷` with `|>`. Examples
include the following:
- `|={E1,E2}=* P` for `|={E1,E2}=∗`
- `P ={E}=* Q` for `P ={E}=∗ Q`
- `P ={E1,E2}=* Q` for `P ={E1,E2}=∗ Q`
- `|={E1}[E2]|>=> Q` for `|={E1}[E2]▷=> Q`
The full list can be found in [theories/bi/ascii.v](theories/bi/ascii.v),
where the ASCII notations are defined in terms of the unicode notations.
* Add affine, absorbing, persistent and timeless instances for telescopes.
* Add a construction `bi_rtc` to create reflexive transitive closures of
PROP-level binary relations.
* Slightly strengthen the lemmas `big_sepL_nil'`, `big_sepL2_nil'`,
`big_sepM_nil'` `big_sepM2_empty'`, `big_sepS_empty'`, and `big_sepMS_empty'`.
They now only require that the argument `P` is affine instead of the whole BI
being affine.
* Add `big_sepL_insert_acc`, a variant of `big_sepL_lookup_acc` which allows
updating the value.
* Add many missing `Proper`/non-expansiveness lemmas for big-ops.
* Add `big_*_insert_delete` lemmas to split a `<[i:=x]> m` map into `i` and the rest.
* Seal the definitions of `big_opS`, `big_opMS`, `big_opM` and `big_sepM2`
to prevent undesired simplification.
* Fix `big_sepM2_fmap*` only working for `nat` keys.

**Changes in `proofmode`:**

* Make use of `notypeclasses refine` in the implementation of `iPoseProof` and
`iAssumption`, see <https://gitlab.mpi-sws.org/iris/iris/merge_requests/329>.
This has two consequences:
1. Coq's "new" unification algorithm (the one in `refine`, not the "old" one
in `apply`) is used more often by the proof mode tactics.
2. Due to the use of `notypeclasses refine`, TC constraints are solved less
eagerly, see <https://github.com/coq/coq/issues/6583>.
In order to port your development, it is often needed to instantiate evars
explicitly (since TC search is performed less eagerly), and in few cases it is
needed to unfold definitions explicitly (due to new unification algorithm
behaving differently).
* Strengthen the tactics `iDestruct`, `iPoseProof`, and `iAssert`:
- They succeed in certain cases where they used to fail.
- They keep certain hypotheses in the intuitionistic context, where they were
moved to the spatial context before.
The latter can lead to stronger proof mode contexts, and therefore to
backwards incompatibility. This can usually be fixed by manually clearing some
hypotheses. A more detailed description of the changes can be found in
<https://gitlab.mpi-sws.org/iris/iris/merge_requests/341>.
* Remove the long-deprecated `cofeT` alias (for `ofeT`) and `dec_agree` RA (use
`agree` instead).

* Add `auto` hint for `∗-∗`.
* Add new tactic `iStopProof` to turn the proof mode entailment into an ordinary
Coq goal `big star of context ⊢ proof mode goal`.
* Add new introduction pattern `-# pat` that moves a hypothesis from the
intuitionistic context to the spatial context.
* The tactic `iAssumption` also recognizes assumptions `⊢ P` in the Coq context.
* Better support for telescopes in the proof mode, i.e., all tactics should
recognize and distribute telescopes now.
* The proof mode now supports names for pure facts in intro patterns. Support
requires implementing `string_to_ident`. Without this tactic such patterns
will fail. We provide one implementation using Ltac2 which works with Coq 8.11
and can be installed with opam; see
[iris/string-ident](https://gitlab.mpi-sws.org/iris/string-ident) for details.

**Changes in `algebra`:**

* Remove `Core` type class for defining the total core; it is now always
defined in terms of the partial core. The only user of this type class was the
STS RA.
* The functions `{o,r,ur}Functor_diag` are no longer coercions, and renamed into
`{o,r,ur}Functor_apply` to better match their intent. This fixes "ambiguous
coercion path" warnings.
* Rename `{o,r,ur}Functor_{ne,id,compose,contractive}` into
`{o,r,ur}Functor_map_{ne,id,compose,contractive}`.
* Move derived camera constructions (`frac_auth` and `ufrac_auth`) to the folder
`algebra/lib`.
* Rename `mnat` to `max_nat` and "box" it by creating a separate type for it.
* Move the RAs for `nat` and `positive` and the `mnat` RA into a separate
module. They must now be imported from `From iris.algebra Require Import
numbers`.
* Make names of `f_op`/`f_core` rewrite lemmas more consistent by always making
`_core`/`_op` the suffix:
`op_singleton` → `singleton_op`, `core_singleton` → `singleton_core`,
`discrete_fun_op_singleton` → `discrete_fun_singleton_op`,
`discrete_fun_core_singleton` → `discrete_fun_singleton_core`,
`list_core_singletonM` → `list_singleton_core`,
`list_op_singletonM` → `list_singleton_op`,
`sts_op_auth_frag` → `sts_auth_frag_op`,
`sts_op_auth_frag_up` → `sts_auth_frag_up_op`,
`sts_op_frag` → `sts_frag_op`,
`list_op_length` → `list_length_op`,
`list_core_singletonM` → `list_singletonM_core`,
`list_op_singletonM` → `list_singletonM_op`.
* All list "map singleton" lemmas consistently use `singletonM` in their name:
`list_singleton_valid` → `list_singletonM_valid`,
`list_singleton_core_id` → `list_singletonM_core_id`,
`list_singleton_snoc` → `list_singletonM_snoc`,
`list_singleton_updateP` → `list_singletonM_updateP`,
`list_singleton_updateP'` → `list_singletonM_updateP'`,
`list_singleton_update` → `list_singletonM_update`,
`list_alloc_singleton_local_update` → `list_alloc_singletonM_local_update`.
* Remove `auth_both_op` and rename `auth_both_frac_op` into `auth_both_op`.
* Add lemma `singleton_included : {[ i := x ]} ≼ ({[ i := y ]} ↔ x ≡ y ∨ x ≼ y`,
and rename existing asymmetric lemmas (with a singleton on just the LHS):
`singleton_includedN` → `singleton_includedN_l`,
`singleton_included` → `singleton_included_l`,
`singleton_included_exclusive` → `singleton_included_exclusive_l`.

* Add notion `ofe_iso A B` that states that OFEs `A` and `B` are
isomorphic. This is used in the COFE solver.
* Add `{o,r,ur}Functor_oFunctor_compose` for composition of functors.
* Add `pair_op_1` and `pair_op_2` to split a pair where one component is the unit.
* Add derived camera construction `excl_auth A` for `auth (option (excl A))`.
* Make lemma `Excl_included` a bi-implication.
* Make `auth_update_core_id` work with any fraction of the authoritative
element.
* Add `min_nat`, an RA for natural numbers with `min` as the operation.
* Add many missing `Proper`/non-expansiveness lemmas for maps and lists.
* Add `list_singletonM_included` and `list_lookup_singletonM_{lt,gt}` lemmas
about singletons in the list RA.
* Add `list_core_id'`, a stronger version of `list_core_id` which only talks
about elements that are actually in the list.

The following `sed` script helps adjust your code to the renaming (on macOS,
replace `sed` by `gsed`, installed via e.g. `brew install gnu-sed`).
Note that the script is not idempotent, do not run it twice.
```
sed -i -E '
# functor renames
s/\b(o|r|ur)Functor_(ne|id|compose|contractive)\b/\1Functor_map_\2/g
# singleton_included renames
s/\bsingleton_includedN\b/singleton_includedN_l/g
s/\bsingleton_included\b/singleton_included_l/g
s/\bsingleton_included_exclusive\b/singleton_included_exclusive_l/g
# f_op/f_core renames
s/\b(op|core)_singleton\b/singleton_\1/g
s/\bdiscrete_fun_(op|core)_singleton\b/discrete_fun_singleton_\1/g
s/\bsts_op_(auth_frag|auth_frag_up|frag)\b/sts_\1_op/g
s/\blist_(op|core)_singletonM\b/list_singletonM_\1/g
s/\blist_op_length\b/list_length_op/g
# list "singleton map" renames
s/\blist_singleton_valid\b/list_singletonM_valid/g
s/\blist_singleton_core_id\b/list_singletonM_core_id/g
s/\blist_singleton_snoc\b/list_singletonM_snoc/g
s/\blist_singleton_updateP\b/list_singletonM_updateP/g
s/\blist_singleton_update\b/list_singletonM_update/g
s/\blist_alloc_singleton_local_update\b/list_alloc_singletonM_local_update/g
# inv renames
s/\binv_sep(|_1|_2)\b/inv_split\1/g
s/\binv_acc\b/inv_alter/g
s/\binv_open(|_strong|_timeless)\b/inv_acc\1/g
s/\bcinv_open(|_strong)\b/cinv_acc\1/g
s/\b(na_inv|auth|sts)_open\b/\1_acc/g
# miscellaneous
s/\bauth_both_frac_op\b/auth_both_op/g
s/\bmnat\b/max_nat/g
s/\bcoreP_wand\b/coreP_entails/g
' $(find theories -name "*.v")
```

## Iris 3.2.0 (released 2019-08-29)

The highlight of this release is the completely re-engineered interactive proof
mode. Not only did many tactics become more powerful; the entire proof mode can
now be used not just for Iris but also for other separation logics satisfying
the proof mode interface (e.g., [Iron] and [GPFSL]). Also see the
[accompanying paper][MoSeL].

[Iron]: https://iris-project.org/iron/
[GPFSL]: https://gitlab.mpi-sws.org/iris/gpfsl/
[MoSeL]: https://iris-project.org/mosel/

Beyond that, the Iris program logic gained the ability to reason about
potentially stuck programs, and a significantly strengthened adequacy theorem
that unifies the three previously separately presented theorems. There are now
also Hoare triples for total program correctness (but with very limited support
for invariants) and logical atomicity.

And finally, our example language HeapLang was made more realistic
(Compare-and-set got replaced by compare-exchange and limited to only compare
values that can actually be compared atomically) and more powerful, with added
support for arrays and prophecy variables.

Further details are given in the changelog below.

This release of Iris received contributions by Aleš Bizjak, Amin Timany, Dan
Frumin, Glen Mével, Hai Dang, Hugo Herbelin, Jacques-Henri Jourdan, Jan Menz,
Jan-Oliver Kaiser, Jonas Kastberg Hinrichsen, Joseph Tassarotti, Mackie Loeffel,
Marianna Rapoport, Maxime Dénès, Michael Sammler, Paolo G. Giarrusso,
Pierre-Marie Pédrot, Ralf Jung, Robbert Krebbers, Rodolphe Lepigre, and Tej
Chajed. Thanks a lot to everyone involved!

**Changes in the theory of Iris itself:**

* Change in the definition of WP, so that there is a fancy update between
the quantification over the next states and the later modality. This makes it
possible to prove more powerful lifting lemmas: The new versions feature an
"update that takes a step".
* Add weakest preconditions for total program correctness.
* "(Potentially) stuck" weakest preconditions and the "plainly modality" are no
longer considered experimental.
* Add the notion of an "observation" to the language interface, so that
every reduction step can optionally be marked with an event, and an execution
trace has a matching list of events. Change WP so that it is told the entire
future trace of observations from the beginning.
* The Löb rule is now a derived rule; it follows from later-intro, later
being contractive and the fact that we can take fixpoints of contractive
functions.
* Add atomic updates and logically atomic triples, including tactic support.
See `heap_lang/lib/increment.v` for an example.
* Extend the state interpretation with a natural number that keeps track of
the number of forked-off threads, and have a global fixed proposition that
describes the postcondition of each forked-off thread (instead of it being
`True`).
* A stronger adequacy statement for weakest preconditions that involves
the final state, the post-condition of forked-off threads, and also applies if
the main-thread has not terminated.
* The user-chosen functor used to instantiate the Iris logic now goes from
COFEs to Cameras (it was OFEs to Cameras).

**Changes in heap_lang:**

* CAS (compare-and-set) got replaced by CmpXchg (compare-exchange). The
difference is that CmpXchg returns a pair consisting of the old value and a
boolean indicating whether the comparison was successful and hence the
exchange happened. CAS can be obtained by simply projecting to the second
component, but also providing the old value more closely models the primitive
typically provided in systems languages (C, C++, Rust).
The comparison by this operation also got weakened to be efficiently
implementable: CmpXchg may only be used to compare "unboxed" values that can
be represented in a single machine word. It is sufficient if one of the two
compared values is unboxed.
* For consistency, the restrictions CmpXchg imposes on comparison also apply to
the `=` binary operator. This also fixes the long-standing problem that that
operator allowed compared closures with each other.
* Implement prophecy variables using the new support for "observations". The
erasure theorem (showing that prophecy variables do not alter program
behavior) can be found [in the iris/examples repository][prophecy-erasure].
* heap_lang now uses right-to-left evaluation order. This makes it
significantly easier to write specifications of curried functions.
* heap_lang values are now injected in heap_lang expressions via a specific
constructor of the expr inductive type. This simplifies much the tactical
infrastructure around the language. In particular, this allow us to get rid
the reflection mechanism that was needed for proving closedness, atomicity and
"valueness" of a term. The price to pay is the addition of new
"administrative" reductions in the operational semantics of the language.
* heap_lang now has support for allocating, accessing and reasoning about arrays
(continuously allocated regions of memory).
* One can now assign "meta" data to heap_lang locations.

[prophecy-erasure]: https://gitlab.mpi-sws.org/iris/examples/blob/3f33781fe6e19cfdb25259c8194d34403f1134d5/theories/logatom/proph_erasure.v

**Changes in Coq:**

* An all-new generalized proof mode that abstracts away from Iris! Major new
features:
- The proof mode can now be used with logics derived from Iris (like iGPS),
with non-step-indexed logics and even with non-affine (i.e., linear) logics.
- `iModIntro` is more flexible and more powerful, it now also subsumes
`iNext` and `iAlways`.
- General infrastructure for deriving a logic for monotone predicates over
an existing logic (see the paper for more details).
Developments instantiating the proof mode typeclasses may need significant
changes. For developments just using the proof mode tactics, porting should
not be too much effort. Notable things to port are:
- All the BI laws moved from the `uPred` module to the `bi` module. For
example, `uPred.later_equivI` became `bi.later_equivI`.
- Big-ops are automatically imported, imports of `iris.base_logic.big_op` have
to be removed.
- The ⊢ notation can sometimes infer different (but convertible) terms when
searching for the BI to use, which (due to Coq limitations) can lead to
failing rewrites, in particular when rewriting at function types.
* The `iInv` tactic can now be used without the second argument (the name for
the closing update). It will then instead add the obligation to close the
invariant to the goal.
* The new `iEval` tactic can be used to execute a simplification or rewriting
tactic on some specific part(s) of the proofmode goal.
* Added support for defining derived connectives involving n-ary binders using
telescopes.
* The proof mode now more consistently "prettifies" the goal after each tactic.
Prettification also simplifies some BI connectives, like conditional
modalities and telescope quantifiers.
* Improved pretty-printing of Iris connectives (in particular WP and fancy
updates) when Coq has to line-wrap the output. This goes hand-in-hand with an
improved test suite that also tests pretty-printing.
* Added a `gmultiset` RA.
* Rename `timelessP` → `timeless` (projection of the `Timeless` class)
* The CMRA axiom `cmra_extend` is now stated in `Type`, using `sigT` instead of
in `Prop` using `exists`. This makes it possible to define the function space
CMRA even for an infinite domain.
* Rename proof mode type classes for laters:
- `IntoLaterN` → `MaybeIntoLaterN` (this one _may_ strip a later)
- `IntoLaterN'` → `IntoLaterN` (this one _should_ strip a later)
- `IntoLaterNEnv` → `MaybeIntoLaterNEnv`
- `IntoLaterNEnvs` → `MaybeIntoLaterNEnvs`
* Rename:
- `frag_auth_op` → `frac_auth_frag_op`
- `cmra_opM_assoc` → `cmra_op_opM_assoc`
- `cmra_opM_assoc_L` → `cmra_op_opM_assoc_L`
- `cmra_opM_assoc'` → `cmra_opM_opM_assoc`
* `namespaces` has been moved to std++.
* Changed `IntoVal` to be directly usable for rewriting `e` into `of_val v`, and
changed `AsVal` to be usable for rewriting via the `[v <-]` destruct pattern.
* `wp_fork` is now written in curried form.
* `PureExec`/`wp_pure` now supports taking multiple steps at once.
* A new tactic, `wp_pures`, executes as many pure steps as possible, excluding
steps that would require unlocking subterms. Every impure wp_ tactic executes
this tactic before doing anything else.
* Add `big_sepM_insert_acc`.
* Add big separating conjunctions that operate on pairs of lists (`big_sepL2`)
and on pairs of maps (`big_sepM2`). In the former case the lists are required
to have the same length, and in the latter case the maps are required to
have the same domains.
* The `_strong` lemmas (e.g. `own_alloc_strong`) work for all infinite
sets, instead of just for cofinite sets. The versions with cofinite
sets have been renamed to use the `_cofinite` suffix.
* Remove locked value lambdas. The value scope notations `rec: f x := e` and
`(λ: x, e)` no longer add a `locked`. Instead, we made the `wp_` tactics
smarter to no longer unfold lambdas/recs that occur behind definitions.
* Export the fact that `iPreProp` is a COFE.
* The CMRA `auth` now can have fractional authoritative parts. So now `auth` has
3 types of elements: the fractional authoritative `●{q} a`, the full
authoritative `● a ≡ ●{1} a`, and the non-authoritative `◯ a`. Updates are
only possible with the full authoritative element `● a`, while fractional
authoritative elements have agreement: `✓ (●{p} a ⋅ ●{q} b) ⇒ a ≡ b`. As a
consequence, `auth` is no longer a COFE and does not preserve Leibniz
equality.
* Add a COFE construction (and functor) on dependent pairs `sigTO`, dual to
`discrete_funO`.
* Rename in `auth`:
- Use `auth_auth_proj`/`auth_frag_proj` for the projections of `auth`:
`authoritative` → `auth_auth_proj` and `auth_own` → `auth_frag_proj`.
- Use `auth_auth` and `auth_frag` for the injections into authoritative
elements and non-authoritative elements respectively.
- Lemmas for the projections and injections are renamed accordingly.
For examples:
+ `authoritative_validN` → `auth_auth_proj_validN`
+ `auth_own_validN` → `auth_frag_proj_validN`
+ `auth_auth_valid` was not renamed because it was already used for the
authoritative injection.
- `auth_both_valid` → `auth_both_valid_2`
- `auth_valid_discrete_2` → `auth_both_valid`
* Add the camera `ufrac` for unbounded fractions (i.e. without fractions that
can be `> 1`) and the camera `ufrac_auth` for a variant of the authoritative
fractional camera (`frac_auth`) with unbounded fractions.
* Changed `frac_auth` notation from `●!`/`◯!` to `●F`/`◯F`. sed script:
`s/◯!/◯F/g; s/●!/●F/g;`.
* Lemma `prop_ext` works in both directions; its default direction is the
opposite of what it used to be.
* Make direction of `f_op` rewrite lemmas more consistent: Flip `pair_op`,
`Cinl_op`, `Cinr_op`, `cmra_morphism_op`, `cmra_morphism_pcore`,
`cmra_morphism_core`.
* Rename lemmas `fupd_big_sep{L,M,S,MS}` into `big_sep{L,M,S,MS}_fupd` to be
consistent with other such big op lemmas. Also add such lemmas for `bupd`.
* Rename `C` suffixes into `O` since we no longer use COFEs but OFEs. Also
rename `ofe_fun` into `discrete_fun` and the corresponding notation `-c>` into
`-d>`. The renaming can be automatically done using the following script
(on macOS, replace `sed` by `gsed`, installed via e.g. `brew install gnu-sed`):
```
sed -i '
s/\bCofeMor/OfeMor/g;
s/\-c>/\-d>/g;
s/\bcFunctor/oFunctor/g;
s/\bCFunctor/OFunctor/g;
s/\b\%CF/\%OF/g;
s/\bconstCF/constOF/g;
s/\bidCF/idOF/g
s/\bdiscreteC/discreteO/g;
s/\bleibnizC/leibnizO/g;
s/\bunitC/unitO/g;
s/\bprodC/prodO/g;
s/\bsumC/sumO/g;
s/\bboolC/boolO/g;
s/\bnatC/natO/g;
s/\bpositiveC/positiveO/g;
s/\bNC/NO/g;
s/\bZC/ZO/g;
s/\boptionC/optionO/g;
s/\blaterC/laterO/g;
s/\bofe\_fun/discrete\_fun/g;
s/\bdiscrete\_funC/discrete\_funO/g;
s/\bofe\_morC/ofe\_morO/g;
s/\bsigC/sigO/g;
s/\buPredC/uPredO/g;
s/\bcsumC/csumO/g;
s/\bagreeC/agreeO/g;
s/\bauthC/authO/g;
s/\bnamespace_mapC/namespace\_mapO/g;
s/\bcmra\_ofeC/cmra\_ofeO/g;
s/\bucmra\_ofeC/ucmra\_ofeO/g;
s/\bexclC/exclO/g;
s/\bgmapC/gmapO/g;
s/\blistC/listO/g;
s/\bvecC/vecO/g;
s/\bgsetC/gsetO/g;
s/\bgset\_disjC/gset\_disjO/g;
s/\bcoPsetC/coPsetO/g;
s/\bgmultisetC/gmultisetO/g;
s/\bufracC/ufracO/g
s/\bfracC/fracO/g;
s/\bvalidityC/validityO/g;
s/\bbi\_ofeC/bi\_ofeO/g;
s/\bsbi\_ofeC/sbi\_ofeO/g;
s/\bmonPredC/monPredO/g;
s/\bstateC/stateO/g;
s/\bvalC/valO/g;
s/\bexprC/exprO/g;
s/\blocC/locO/g;
s/\bdec\_agreeC/dec\_agreeO/g;
s/\bgnameC/gnameO/g;
s/\bcoPset\_disjC/coPset\_disjO/g;
' $(find theories -name "*.v")
```

## Iris 3.1.0 (released 2017-12-19)

**Changes in and extensions of the theory:**

* Define `uPred` as a quotient on monotone predicates `M -> SProp`.
* Get rid of some primitive laws; they can be derived:
`True ⊢ □ True` and `□ (P ∧ Q) ⊢ □ (P ∗ Q)`
* Camera morphisms have to be homomorphisms, not just monotone functions.
* Add a proof that `f` has a fixed point if `f^k` is contractive.
* Constructions for least and greatest fixed points over monotone predicates
(defined in the logic of Iris using impredicative quantification).
* Add a proof of the inverse of `wp_bind`.
* [Experimental feature] Add new modality: ■ ("plainly").
* [Experimental feature] Support verifying code that might get stuck by
distinguishing "non-stuck" vs. "(potentially) stuck" weakest
preconditions. (See [Swasey et al., OOPSLA '17] for examples.) The non-stuck
`WP e @ E {{ Φ }}` ensures that, as `e` runs, it does not get stuck. The stuck
`WP e @ E ?{{ Φ }}` ensures that, as usual, all invariants are preserved while
`e` runs, but it permits execution to get stuck. The former implies the
latter. The full judgment is `WP e @ s; E {{ Φ }}`, where non-stuck WP uses
*stuckness bit* `s = NotStuck` while stuck WP uses `s = MaybeStuck`.

**Changes in Coq:**

* Move the `prelude` folder to its own project:
[coq-std++](https://gitlab.mpi-sws.org/robbertkrebbers/coq-stdpp)
* Some extensions/improvements of heap_lang:
- Improve handling of pure (non-state-dependent) reductions.
- Add fetch-and-add (`FAA`) operation.
- Add syntax for all Coq's binary operations on `Z`.
* Generalize `saved_prop` to let the user choose the location of the type-level
later. Rename the general form to `saved_anything`. Provide `saved_prop` and
`saved_pred` as special cases.
* Improved big operators:
+ They are no longer tied to cameras, but work on any monoid
+ The version of big operations over lists was redefined so that it enjoys
more definitional equalities.
* Rename some things and change notation:
- The unit of a camera: `empty` -> `unit`, `∅` -> `ε`
- Disjointness: `⊥` -> `##`
- A proof mode type class `IntoOp` -> `IsOp`
- OFEs with all elements being discrete: `Discrete` -> `OfeDiscrete`
- OFE elements whose equality is discrete: `Timeless` -> `Discrete`
- Timeless propositions: `TimelessP` -> `Timeless`
- Camera elements such that `core x = x`: `Persistent` -> `CoreId`
- Persistent propositions: `PersistentP` -> `Persistent`
- The persistent modality: `always` -> `persistently`
- Adequacy for non-stuck weakestpre: `adequate_safe` -> `adequate_not_stuck`
- Consistently SnakeCase identifiers:
+ `CMRAMixin` -> `CmraMixin`
+ `CMRAT` -> `CmraT`
+ `CMRATotal` -> `CmraTotal`
+ `CMRAMorphism` -> `CmraMorphism`
+ `CMRADiscrete` -> `CmraDiscrete`
+ `UCMRAMixin` -> `UcmraMixin`
+ `UCMRAT` -> `UcmraT`
+ `DRAMixin` -> `DraMixin`
+ `DRAT` -> `DraT`
+ `STS` -> `Sts`
- Many lemmas also changed their name. `always_*` became `persistently_*`,
and furthermore: (the following list is not complete)
+ `impl_wand` -> `impl_wand_1` (it only involves one direction of the
equivalent)
+ `always_impl_wand` -> `impl_wand`
+ `always_and_sep_l` -> `and_sep_l`
+ `always_and_sep_r` -> `and_sep_r`
+ `always_sep_dup` -> `sep_dup`
+ `wand_impl_always` -> `impl_wand_persistently` (additionally,
the direction of this equivalence got swapped for consistency's sake)
+ `always_wand_impl` -> `persistently_impl_wand` (additionally, the
direction of this equivalence got swapped for consistency's sake)
The following `sed` snippet should get you most of the way (on macOS you will
have to replace `sed` by `gsed`, installed via e.g. `brew install gnu-sed`):
```
sed -i 's/\bPersistentP\b/Persistent/g; s/\bTimelessP\b/Timeless/g; s/\bCMRADiscrete\b/CmraDiscrete/g; s/\bCMRAT\b/CmraT/g; s/\bCMRAMixin\b/CmraMixin/g; s/\bUCMRAT\b/UcmraT/g; s/\bUCMRAMixin\b/UcmraMixin/g; s/\bSTS\b/Sts/g' $(find -name "*.v")
```
* `PersistentL` and `TimelessL` (persistence and timelessness of lists of
propositions) are replaces by `TCForall` from std++.
* Fix a bunch of consistency issues in the proof mode, and make it overall more
usable. In particular:
- All proof mode tactics start the proof mode if necessary; `iStartProof` is
no longer needed and should only be used for building custom proof mode
tactics.
- Change in the grammar of specialization patterns: `>[...]` -> `[> ...]`
- Various new specification patterns for `done` and framing.
- There is common machinery for symbolic execution of pure reductions. This
is provided by the type classes `PureExec` and `IntoVal`.
- There is a new connective `tc_opaque`, which can be used to make definitions
opaque for type classes, and thus opaque for most tactics of the proof
mode.
- Define Many missing type class instances for distributing connectives.
- Implement the tactics `iIntros (?)` and `iIntros "!#"` (i.e. `iAlways`)
using type classes. This makes them more generic, e.g., `iIntros (?)` also
works when the universal quantifier is below a modality, and `iAlways` also
works for the plainness modality. A breaking change, however, is that these
tactics now no longer work when the universal quantifier or modality is
behind a type class opaque definition. Furthermore, this can change the
name of anonymous identifiers introduced with the "%" pattern.
* Make `ofe_fun` dependently typed, subsuming `iprod`. The latter got removed.
* Define the generic `fill` operation of the `ectxi_language` construct in terms
of a left fold instead of a right fold. This gives rise to more definitional
equalities.
* The language hierarchy (`language`, `ectx_language`, `ectxi_language`) is now
fully formalized using canonical structures instead of using a mixture of
type classes and canonical structures. Also, it now uses explicit mixins. The
file `program_logic/ectxi_language` contains some documentation on how to
setup Iris for your language.
* Restore the original, stronger notion of atomicity alongside the weaker
notion. These are `Atomic a e` where the stuckness bit `s` indicates whether
expression `e` is weakly (`a = WeaklyAtomic`) or strongly
(`a = StronglyAtomic`) atomic.
* Various improvements to `solve_ndisj`.
* Use `Hint Mode` to prevent Coq from making arbitrary guesses in the presence
of evars, which often led to divergence. There are a few places where type
annotations are now needed.
* The rules `internal_eq_rewrite` and `internal_eq_rewrite_contractive` are now
stated in the logic, i.e., they are `iApply`-friendly.

## Iris 3.0.0 (released 2017-01-11)

* There now is a deprecation process. The modules `*.deprecated` contain
deprecated notations and definitions that are provided for backwards
compatibility and will be removed in a future version of Iris.
* View shifts are radically simplified to just internalize frame-preserving
updates. Weakestpre is defined inside the logic, and invariants and view
shifts with masks are also coded up inside Iris. Adequacy of weakestpre is
proven in the logic. The old ownership of the entire physical state is
replaced by a user-selected predicate over physical state that is maintained
by weakestpre.
* Use OFEs instead of COFEs everywhere. COFEs are only used for solving the
recursive domain equation. As a consequence, CMRAs no longer need a proof of
completeness. (The old `cofeT` is provided by `algebra.deprecated`.)
* Implement a new agreement construction. Unlike the old one, this one
preserves discreteness. dec_agree is thus no longer needed and has been moved
to algebra.deprecated.
* Renaming and moving things around: uPred and the rest of the base logic are in
`base_logic`, while `program_logic` is for everything involving the general
Iris notion of a language.
* Renaming in prelude.list: Rename `prefix_of` -> `prefix` and `suffix_of` ->
`suffix` in lemma names, but keep notation ``l1 `prefix_of` l2`` and ``l1
`suffix_of` l2``. `` l1 `sublist` l2`` becomes ``l1 `sublist_of` l2``. Rename
`contains` -> `submseteq` and change `` l1 `contains` l2`` to ``l1 ⊆+ l2``.
* Slightly weaker notion of atomicity: an expression is atomic if it reduces in
one step to something that does not reduce further.
* Changed notation for embedding Coq assertions into Iris. The new notation is
⌜φ⌝. Also removed `=` and `⊥` from the Iris scope. (The old notations are
provided in `base_logic.deprecated`.)
* Up-closure of namespaces is now a notation (↑) instead of a coercion.
* With invariants and the physical state being handled in the logic, there is no
longer any reason to demand the CMRA unit to be discrete.
* The language can now fork off multiple threads at once.
* Local Updates (for the authoritative monoid) are now a 4-way relation with
syntax-directed lemmas proving them.

## Iris 2.0

* [heap_lang] No longer use dependent types for expressions. Instead, values
carry a proof of closedness. Substitution, closedness and value-ness proofs
are performed by computation after reflecting into a term langauge that knows
about values and closed expressions.
* [program_logic/language] The language does not define its own "atomic"
predicate. Instead, atomicity is defined as reducing in one step to a value.
* [program_logic] Due to a lack of maintenance and usefulness, lifting lemmas
for Hoare triples are removed.

## Iris 2.0-rc2

This version matches the final ICFP 2016 paper.

* [algebra] Make the core of an RA or CMRA a partial function.
* [program_logic/lifting] Lifting lemmas no longer round-trip through a
user-chosen predicate to define the configurations we can reduce to; they
directly relate to the operational semantics. This is equivalent and
much simpler to read.

## Iris 2.0-rc1

This is the Coq development and Iris Documentation as submitted to ICFP 2016.