proposition: Lemma ctree_sub_cons t1 t2 t3 et : ctree_sub (ctree_cons t1 t2 t3) et = ctree_sub (CtreeNode t1 t2 t3) et.
proof: Proof. rewrite ctree_cons_spec; case: ctree_empty_nodeP => // ->. by case: et => [|[] et]. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq) fourcolor(color)