proposition: Fact joinA : associative join.
proof: Proof. by elim=> [|? ? ih] [|? ?] [|? ?] //=; rewrite joinA ih. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)