A method of Feynman diagrams summation, based on using Schwinger-Dyson
equations and Ward identities, is verified by calculating some four-loop
diagrams in N=1 supersymmetric electrodynamics, regularized by higher
derivatives. In particular, for the considered diagrams correctness of an
additional identity for Green functions, which is not reduced to the gauge Ward
identity, is proved.Comment: 14 pages, 9 figure