Popivanov, P.; Kutev, N. Viscosity solutions to the degenerate oblique derivative problem for fully nonlinear elliptic equations. (English) Zbl 1101.35035 Math. Nachr. 278, No. 7-8, 888-903 (2005). Reviewer: Vesa Mustonen (Oulu) MSC: 35J65 35J70 PDFBibTeX XMLCite \textit{P. Popivanov} and \textit{N. Kutev}, Math. Nachr. 278, No. 7--8, 888--903 (2005; Zbl 1101.35035) Full Text: DOI
Popivanov, P.; Kutev, N. On the solvability of equations with prescribed Gauss curvature changing its sign. (English) Zbl 0674.35014 Math. Nachr. 137, 159-165 (1988). Reviewer: P.Popivanov MSC: 35G30 53A10 35A05 35B65 35A30 PDFBibTeX XMLCite \textit{P. Popivanov} and \textit{N. Kutev}, Math. Nachr. 137, 159--165 (1988; Zbl 0674.35014) Full Text: DOI
Gramchev, Todor V.; Popivanov, Peter R. Singularities of the solutions of non-correct mixed problems for second order strictly hyperbolic operators. (English) Zbl 0577.35070 Math. Nachr. 121, 53-60 (1985). Reviewer: M.Idemen MSC: 35L20 35L67 35A05 PDFBibTeX XMLCite \textit{T. V. Gramchev} and \textit{P. R. Popivanov}, Math. Nachr. 121, 53--60 (1985; Zbl 0577.35070) Full Text: DOI