proposition: Lemma iter_fix T n f (x : T) : f x = x -> iter n f x = x.
proof: Proof. by move=> fixf; elim: n => //= n ->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)