1. Mathematical Surveys, No. 5;Bergman, Stefan,1950
2. Kernel functions and conformal mapping;Bergman, S.;Compositio Math.,1951
3. R. de Possel, Zum Parallelschlitztheorem unendlichvielfach zusammenhaengender Gebiete, Göttinger Nachrichten (1931) pp. 199-202.
4. Identities in the theory of conformal mapping;Garabedian, P. R.;Trans. Amer. Math. Soc.,1949
5. G. M. Golusin, Rec. Math. N.S. vol. 3 (45) (1938) pp. 321-330.