Commit 3f5c467b authored by Robbert Krebbers's avatar Robbert Krebbers
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Comment about `AsFractional` instances.

parent fb763c47
......@@ -70,6 +70,16 @@ Section fractional.
Persistent P TCOr (Affine P) (Absorbing P) Fractional (λ _, P).
Proof. intros ?? q q'. apply: bi.persistent_sep_dup. Qed.
(** We do not have [AsFractional] instances for [∗] and the big operators
because the [iDestruct] tactic already turns [P ∗ Q] into [P] and [Q],
[[∗ list] k↦x ∈ y :: l, Φ k x] into [Φ 0 i] and [[∗ list] k↦x ∈ l, Φ (S k) x],
etc. Hence, an [AsFractional] instance would cause ambiguity because for
example [l ↦{1} v ∗ l' ↦{1} v'] could be turned into [l ↦{1} v] and
[l' ↦{1} v'], or into two times [l ↦{1/2} v ∗ l' ↦{1/2} v'].
We do provide the [Fractional] instances so that when one defines a derived
connection in terms of [∗] or a big operator (and makes that opaque in some
way), one could choose to split along the [∗] or along the fraction. *)
Global Instance fractional_sep Φ Ψ :
Fractional Φ Fractional Ψ Fractional (λ q, Φ q Ψ q)%I.
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