proposition: Lemma setDidPl A B : reflect (A :\: B = A) [disjoint A & B].
proof: Proof. by rewrite setDE disjoints_subset; apply: setIidPl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)