Instead, I have introduced a type class `Monoid` that is used by the big operators:

    Class Monoid {M : ofeT} (o : M → M → M) := {
      monoid_unit : M;
      monoid_ne : NonExpansive2 o;
      monoid_assoc : Assoc (≡) o;
      monoid_comm : Comm (≡) o;
      monoid_left_id : LeftId (≡) monoid_unit o;
      monoid_right_id : RightId (≡) monoid_unit o;
    }.

Note that the operation is an argument because we want to have multiple monoids over
the same type (for example, on `uPred`s we have monoids for `∗`, `∧`, and `∨`). However,
we do bundle the unit because:

- If we would not, the unit would appear explicitly in an implicit argument of the
  big operators, which confuses rewrite. By bundling the unit in the `Monoid` class
  it is hidden, and hence rewrite won't even see it.
- The unit is unique.

We could in principle have big ops over setoids instead of OFEs. However, since we do
not have a canonical structure for bundled setoids, I did not go that way.

This patch was created using

  find -name *.v | xargs -L 1 awk -i inplace '{from = 0} /^From/{ from = 1; ever_from = 1} { if (from == 0 && seen == 0 && ever_from == 1) { print "Set Default Proof Using \"Type*\"."; seen = 1 } }1 '

and some minor manual editing

The rewrite auth_validN_eq was not performed in the hypothesis. It
used to work in 8.5 because of magic.

Also, use explicit unfolding lemmas for auth_valid and auth_validN.
The `Arguments valid _ _ !_ /` hack did not really work when one
has to deal with the valid instance of the cmra, which underneath also
includes a `cmra_valid`. Declaring a similar Arguments for `cmra_valid`
is a bad idea, it will also end up unfold stuff for the exclusive and
option CMRA.

Proof was done by Hai & me

Use COFEs only for the recursive domain equation solver

This allows us to factor out properties about connectives that
commute with the big operators.

This requirement was useful in Iris 2.0: in order to ensure that ownership of
the physical state was timeless, we required the ghost CMRA to have a timeless
unit. To avoid having additional type class parameters, or having to extend the
algebraic hierarchy, we required the units of any CMRA to be timeless.

In Iris 3.0, this issue no longer applies: ownership of the physical state is
ghost ownership in the global CMRA, whose unit is always timeless.

Thanks to Jeehoon Kang for spotting this unnecessary requirement.

This is more consistent with the definition of the extension order, which
is also defined in terms of an existential.

This is to avoid confusion with ghost_ownership.own.

be the same as .

This is a fairly intrusive change, but at least makes notations more
consistent, and often shorter because fewer parentheses are needed. Note
that viewshifts already had the same precedence as →.

Based on an idea and WIP commits of J-H. Jourdan: the core of a CMRA
A is now a partial function A → option A.

TODO: define sum CMRA
TODO: remove one shot CMRA and define it in terms of sum

- Make the carrier argument of the constructors for the canonical structures
  cofeT and cmraT explicit. This way we make sure the carrier is properly
  exposed, instead of some alias of the carrier.
- Make derived constructions (such as discreteC and discreteR) notations
  instead of definitions. This is yet again to make sure that the carrier is
  properly exposed.
- Turn DRA into a canonical structure (it used to be a type class).

This fixes some issues, notably it fixes some broken rewrites in algebra/sts
and it makes canonical structures work properly with dec_agree.