1. The boundary-value problem for a first order elliptic system in the plane;Vinogradov;Differential Equations,1971
2. On a method of investigating singular integral equations in a bounded plane region;Džuraev;Soviet Math. Dokl.,1971
3. 3 Bojarski B. . Investigations of elliptic systems in the plane (Doctoral dissertation, Moscow, 1960) (Russian).