1. Bers L., John L., Schechter L.,Partial Differential Equations, Interscience (1964).
2. Buonocore P., Manselli P.,Nonunique Continuation for Plane Uniformly Elliptic Equations in Sobolev Spaces, Ann. Scuola Norm. Sup. Pisa - Serie IV. Vol. XXIX. Fasc. 4 (2000), 731–754.
3. Cavazzoni R.,On the Cauchy problem for elliptic equations in a disk, Rend. Circ. Mat. Palermo (2),52 (2003), 131–140.
4. Gilbarg R., Trudinger N. S.,Elliptic partial differential equations of second order, Springer-Verlag.
5. Hormander L.,An introduction to complex analysis, D. Van Nostrand Company Inc. (Princeton, New Jersey), 1967.