Semerdzhiev, Khr. A method for simultaneous determination of all roots of an algebraic equation when their multiplicities are given. (Russian) Zbl 0516.65023 C. R. Acad. Bulg. Sci. 35, 1057-1060 (1982). MSC: 65H05 26C10 30C15 PDFBibTeX XMLCite \textit{Khr. Semerdzhiev}, C. R. Acad. Bulg. Sci. 35, 1057--1060 (1982; Zbl 0516.65023)
Boev, T. B. On the propagation of singularities for operators with involutive characteristics. (English) Zbl 0434.35091 C. R. Acad. Bulg. Sci. 33, 39-42 (1980). MSC: 35S99 35B45 35A07 35B65 58J47 47Gxx PDFBibTeX XMLCite \textit{T. B. Boev}, C. R. Acad. Bulg. Sci. 33, 39--42 (1980; Zbl 0434.35091)