1. H. Begehr, Complex Analytic Methods for Partial Differential Equations: an Introductory Text, World Scientific Publ., River Edge, NJ (1994).
2. H. Begehr, “Boundary value problems in complex analysis, I,” Bol. Asoc. Mat. Venez., 12, 65–85 (2005).
3. H. Begehr and G. Harutjunjan, “Robin boundary value problem for the Cauchy–Riemann operator,” Complex Var. Elliptic Equat., 50, No. 15, 1125–1136 (2005).
4. H. Begehr and G. Harutjunjan, “Robin boundary value problem for the Poisson equation,” J. Anal. Appl., 4, No. 3, 201–213 (2006).
5. H. Begehr and G. Harutjunjan, “Neumann problem for the Beltrami operator and for second order operators with Poisson–Bitsadze operator as main part,” Complex Var. Elliptic Equat., 54, No. 12, 1129–1150 (2009).