proposition: Lemma diso_compl (G : sgraph) : compl (compl G) ≃ G.
proof: Proof. apply: (@Diso' (compl (compl G)) G id id) => // x y. abstract by rewrite [RHS]/edge_rel/= [in RHS]/edge_rel/= negb_and !negbK; case: eqVneq => /= [->|]; rewrite sgP. Defined.
imports: Coq(Setoid CMorphisms) mathcomp(all_ssreflect) GraphTheory(edone preliminaries bij digraph) GraphTheory(set_tac)