Prove missing fractional_big_sepL2

CHANGELOG.md

@@ -74,6 +74,7 @@ Coq 8.11 is no longer supported in this version of Iris.
   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`:**
 

iris/bi/lib/fractional.v

@@ -82,6 +82,11 @@ Section fractional.
     Fractional (PROP:=PROP) (λ q, [∗ list] k↦x ∈ l, Ψ k x q)%I.
   Proof. intros ? q q'. rewrite -big_sepL_sep. by setoid_rewrite fractional. Qed.
 
+  Global Instance fractional_big_sepL2 {A B} (l1 : list A) (l2 : list B) Ψ :
+    (∀ k x1 x2, Fractional (Ψ k x1 x2)) →
+    Fractional (PROP:=PROP) (λ q, [∗ list] k↦x1; x2 ∈ l1; l2, Ψ k x1 x2 q)%I.
+  Proof. intros ? q q'. rewrite -big_sepL2_sep. by setoid_rewrite fractional. Qed.
+
   Global Instance fractional_big_sepM `{Countable K} {A} (m : gmap K A) Ψ :
     (∀ k (x : A), Fractional (Ψ k x)) →
     Fractional (PROP:=PROP) (λ q, [∗ map] k↦x ∈ m, Ψ k x q)%I.