proposition: Lemma adjoinC V x y : << <<V; x>>; y>>%VS = << <<V; y>>; x>>%VS.
proof: Proof. by rewrite !agenv_add_id -!addvA (addvC <[x]>%VS). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype div tuple finfun bigop ssralg) mathcomp(finalg zmodp matrix vector poly)