“…, . ρ θ ∈Ω (21) Since the integrand function in the integral (20) turns to infinity at the point (ρ 0 , θ 0 ), when finding the derivatives for the expansion of (20), it is necessary to first exclude this point from the region Ω. To this end, the point (ρ 0 , θ 0 ) is cut out of Ω by a circle of radius α.…”