1. Sobolev SL: Some Applications of Functional Analysis in Mathematical Physics. Izdat. Leningrad. Gos. Univ., Leningrad; 1950.
2. Vekua, IN: On metaharmonic functions. Lect. Notes TICMI 14, 62 pp. (2013). Translated from the 1943 Russian original Trav. Inst. Math. Tbilissi 12, 105-174 (1943)
3. Vekua IN: New Methods for Solving Elliptic Equations. OGIZ, Moscow; 1948.
4. Cassisa C, Ricci P, Tavkhelidze I: Analogue of Saint-Venant’s principle for the one special type 4-th order elliptic equation and its applications. Appl. Math. Inform. 1999, 4: 11-29.
5. Kondrat’ev VA, Oleinik OA: Boundary value problems for the system of elasticity theory in unbounded domains. Korn’s inequalities. Usp. Mat. Nauk 1988, 43(5):55-98. (in Russian)