fact: Fixpoint gtr_match1 r := match r with | GtrNil => false | GtrCons _ (CtreeNode (CtreeLeaf _) _ _) _ => true | GtrCons _ _ r' => gtr_match1 r' end.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq) fourcolor(color ctree chromogram gtree)