proposition: Lemma opn_Knm_l n m (x : 'I_n) : N(inl x : 'K_n,m) = [set inr y | y in [set: 'I_m]].
proof: Proof. apply/setP=> -[z|z]; rewrite ?mem_imset ?inE //; last exact: inr_inj. by symmetry; apply: contraTF isT => /imsetP [z']. Qed.
imports: Coq(Setoid CMorphisms) mathcomp(all_ssreflect) GraphTheory(edone preliminaries bij digraph) GraphTheory(set_tac)