V. M. Loktev and V. M. Turkowski, Green function of fermions in 2D superconducting Frohlich model with inhomogeneous order parameter, Low Temp. Phys. 26, (2000) [Fiz. Nizk. Temp. 26, 135-141, (2000)] DOI: https://doi.org/10.1063/1.593871.