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