(* Autor(s): Andrej Dudenhefner (1) Affiliation(s): (1) Saarland University, Saarbrücken, Germany *)
Local Notation "A ≡ B" := (mset_eq A B) (at level 65).
Arguments mset_eq !A !B.
(* solves trivial multiset equalities *)
Ltac eq_trivial :=
move=> ?; rewrite ? (count_occ_app, count_occ_cons, count_occ_nil, eta_reduction); unlock; by lia.

Lemma eq_app_iff {A B C} : (A ++ B) ≡ (A ++ C) <-> B ≡ C.