O(m²(Z)⁶) contribution to Lamb shift from radiative corrections to the Wichmann-Kroll potential

We derive an analytical expression for the contribution of the order m alpha(2)(Z alpha)(6) to the hydrogen Lamb shift which comes from the diagrams for radiative corrections to the Wichmann-Kroll potential. We use modern methods of multiloop calculations, based on IBP reduction, DRA method and differential equations.