Calibration of light cone for N = 2 strings

Due to the extended supersymmetry on the world list the covariant quantization of the self-dual strings in the plane space of the 2+2 signature is reduced to the zero modes consideration. The way of obtaining this result by the dual application of the light cone calibration is indicated. The specific peculiarity of such calibration consists therein, that part of the anticommutation variables is removed from the consideration through the local symmetries with the even parameter. The reducibility of the N = 4 string and its equivalence to the N = 2 string become evident