proposition: Lemma in_mset2 x a b : (x \in [mset a; b]) = (x == a) || (x == b).
proof: Proof. by rewrite !inE. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap