proposition: Lemma eq_finset (pA pB : pred T) : pA =1 pB -> finset pA = finset pB.
proof: Proof. by move=> eq_p; apply/setP => x; rewrite !(in_set, inE) eq_p. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)