proposition: Lemma mem_allpairs_rconsr f s t y0 : [seq f x y | x <- s, y <- rcons (t x) (y0 x)] =i ([seq f x y | x <- s, y <- t x] ++ [seq f x (y0 x) | x <- s]).
proof: Proof. exact/perm_mem/permPl/allpairs_rconsr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)