proposition: Lemma cliqueIstable A C : clique C -> stable A -> #|C :&: A| <= 1.
proof: Proof. move => clique_C; apply: contraTT; rewrite -ltnNge. case/card_gt1P => x [y] [/setIP[xA xC] /setIP[yA yC] xDy]. apply/stablePn; exists x, y; split => //. exact: clique_C. Qed.
imports: mathcomp(all_ssreflect) GraphTheory(preliminaries bij digraph) GraphTheory(sgraph dom partition)