proposition: Fact joinKI y x : meet x (join x y) = x.
proof: Proof. elim: x y => [|? ? ih] [|? ?] //=; rewrite (meetxx, joinKI) ?ih //. by congr cons; rewrite meetss. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)