Bis-[4-(2,2-bis-aethoxycarbonyl-acetylamino)-phenyl]-methan, tetraethyl 2,2'-[methylenebis(4,1-phenyleneiminocarbonyl)]bismalonate, N-{4-[4-(2,2-Bis-ethoxycarbonyl-acetylamino)-benzyl]-phenyl}-2-ethoxycarbonyl-malonamic acid ethyl ester, 2,2'-Bis-aethoxycarbonyl-N,N'-(4,4'-methandiyl-di-phenyl)-bis-malonamidsaeure-diaethylester,