2 citations to https://www.mathnet.ru/rus/tmf3924

1. Hung Jung Lu, “Dressed skeleton expansion in (1+1)-dimensional field-theory models”, Phys. Rev. D, 45:4 (1992), 1217  
2. P. Hählen, “The massive thirring model: Perturbation theory versus the solution of Berezin and Sushko”, Nuclear Physics B, 102:1 (1976), 67