proposition: Lemma index_of_indom : forall A B (M:map A B) k, k \indom M -> index M k.
proof: Proof. Proof using. intros. rewrite~ index_eq_indom. Qed.
imports: TLC(LibTactics LibLogic LibReflect LibOption LibRelation LibLogic LibOperation LibEpsilon LibMonoid LibSet)