Description: The empty graph, with vertices but no edges, is a pseudograph. (Contributed by Mario Carneiro, 12-Mar-2015) (Revised by AV, 11-Oct-2020) (Proof shortened by AV, 25-Nov-2020)
|- ( ph -> G e. W )
|- ( ph -> ( iEdg ` G ) = (/) )
|- ( ph -> G e. UPGraph )
|- ( ph -> G e. UMGraph )
|- ( G e. UMGraph -> G e. UPGraph )