proposition: Lemma bound_joinC : commutative bound_join.
proof: Proof. case=> [? ?|[]][? ?|[]] //=; rewrite joinC; congr BSide. by case: lcomparableP; rewrite ?andbT // andbC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(div fintype bigop order ssralg finset fingroup) mathcomp(ssrnum)