. . . . . . . "An electron-withdrawing group, as used herein, refers to an atom or group having a (+) value, including halogen atoms such as fluorine atoms, a chlorine atom and a bromine atom, a trifluoromethyl group, a trichloromethyl group, a tribromomethyl group, a nitro group, a nitrile group, alkoxyl groups such as a methoxyl group and an ethoxyl group, a carboxyl group, alkylcarbonyl groups such as a methy" .