proposition: Lemma cpN_trans a x z y : a \notin cp x z -> a \notin cp z y -> a \notin cp x y.
proof: Proof. Proof using. move => /negbTE A /negbTE B. apply/negP. move/(subsetP (cp_triangle z)). by rewrite !inE A B. Qed.
imports: mathcomp(all_ssreflect) GraphTheory(edone preliminaries digraph) GraphTheory(sgraph connectivity)