fact: Definition ctree_empty_node t := match t with | CtreeNode CtreeEmpty CtreeEmpty CtreeEmpty => true | CtreeNode _ CtreeEmpty CtreeEmpty => false | CtreeNode _ _ CtreeEmpty => false | _ => false end.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq) fourcolor(color)