(concurring). I am constrained to concur; however, disputes of this nature between “unclean” parties would seem to come very close to requiring, with respect to the defendant Nathan’s counterclaim, that “a court of equity should withhold its aid and not become the promoter of wrongdoing.” Johnson v. Yellow Cab Transit Co., 321 U. S. 383, 402 (1944) (Frankfurter, J., dissenting).