proposition: Lemma CK4F_one : CK4F 1.
proof: Proof. split. move => [] [] _ _. exact: connect0. apply small_K_free. by rewrite card_unit. Qed.
imports: Coq(RelationClasses Morphisms Setoid Lia) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries) GraphTheory(digraph sgraph minor checkpoint cp_minor) GraphTheory(setoid_bigop structures pttdom ptt) GraphTheory(mgraph mgraph2 skeleton bounded)