proposition: Lemma adjoin_cons V x rs : <<V & x :: rs>>%VS = << <<V; x>> & rs>>%VS.
proof: Proof. by rewrite span_cons addvA agenv_add_id. 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)