proposition: Lemma lookup_difference_Some {A} (m1 m2 : M A) i x : (m1 ∖ m2) !! i = Some x ↔ m1 !! i = Some x ∧ m2 !! i = None.
proof: Proof. rewrite lookup_difference. destruct (m1 !! i), (m2 !! i); naive_solver. Qed.
imports: Coq(Permutation) stdpp(options)