reserve G for _Graph;
reserve V for non empty set, E for Relation of V;

theorem Th70:
  E is empty iff createGraph(V,E) is edgeless
proof
  thus E is empty implies createGraph(V,E) is edgeless;
  assume createGraph(V,E) is edgeless;
  then VertexDomRel(createGraph(V,E)) is empty;
  hence thesis;
end;
