proposition: Lemma mem_eq_pblock P A : A \in P -> forall x, x \in A -> pblock P x = A.
proof: Proof. move=> AinP x xinA. exact: (def_pblock (partition_trivIset (setpartP P)) AinP). Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(div ssralg ssrint ssrnum binomial) tools combclass sorted ordtype partition