proposition: Lemma tuto_setD1P : forall x A b, reflect (x != b /\ x \in A) (x \in A :\ b).
proof: Proof. move=> x A b; rewrite !inE; exact: andP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finset)