1. G. Giraud, ?Generalisation des problemes sur les operations du type elliptiques,? Bull. Sci. Math.,60, 316?352 (1932).
2. G. Giraud, ?Problemes de valeurs a la frontiere relatifs a certaines donnees discontinues,? Bull. Soc. Math. France,61, 1?54 (1933).
3. O. A. Oleinik, ?On the properties of the solutions of some boundary problems for equations of elliptic type,? Matem. Sb.,30(3), 695?702 (1952).
4. E. Hopf, ?A remark on linear elliptic differential equations of the second order,? Proc. Amer. Math. Soc.,3, 791?793 (1952).
5. R. Vyborny, ?On the properties of the solutions of some boundary problems for equations of parabolic type,? Dokl. Akad. Nauk SSSR,117, No. 3, 563?565 (1957).