proposition: Lemma ctree_sub_leaf_of n et : ctree_sub (ctree_leaf_of n) et = (if size et == 0 then n else 0).
proof: Proof. by case: et n => [|e et] [] //=; elim=> //= n ->. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq) fourcolor(color)