proposition: Lemma TW2_K4_free (G : sgraph) (T : forest) (B : T -> {set G}) : sdecomp T G B -> width B <= 3 -> K4_free G.
proof: Proof. exact: treewidth_K_free. Qed.
imports: Coq(RelationClasses) mathcomp(all_ssreflect) GraphTheory(edone preliminaries digraph) GraphTheory(sgraph treewidth set_tac)