El-Sayed Ibrahim, Sobhy On boundary conditions for Sturm-Liouville differential operators in the direct sum spaces. (English) Zbl 0954.34018 Rocky Mt. J. Math. 29, No. 3, 873-892 (1999). Reviewer: Paolo Piccione (São Paulo) MSC: 34B24 34L40 PDFBibTeX XMLCite \textit{S. El-Sayed Ibrahim}, Rocky Mt. J. Math. 29, No. 3, 873--892 (1999; Zbl 0954.34018) Full Text: DOI Link
El-Sayed Ibrahim, Sobhy On the essential spectra of regularly solvable operators in the direct sum spaces. (English) Zbl 0947.47004 Rocky Mt. J. Math. 29, No. 2, 609-644 (1999). Reviewer: A.G.Baskakov (Voronezh) MSC: 47A25 47A10 47E05 PDFBibTeX XMLCite \textit{S. El-Sayed Ibrahim}, Rocky Mt. J. Math. 29, No. 2, 609--644 (1999; Zbl 0947.47004) Full Text: DOI Link
El-Sayed Ibrahim, Sobhy Non self-adjoint quasi-differential operators with discrete spectra. (English) Zbl 0881.47024 Rocky Mt. J. Math. 25, No. 3, 1053-1078 (1995). Reviewer: S.Totaro (Firenze) MSC: 47E05 47D06 34L05 47A25 PDFBibTeX XMLCite \textit{S. El-Sayed Ibrahim}, Rocky Mt. J. Math. 25, No. 3, 1053--1078 (1995; Zbl 0881.47024) Full Text: DOI
El-Sayed Ibrahim, Sobhy The point spectra and regularity fields of non-selfadjoint quasi- differential operators. (English) Zbl 0832.47043 Rocky Mt. J. Math. 25, No. 2, 685-699 (1995). MSC: 47E05 47A10 34G20 PDFBibTeX XMLCite \textit{S. El-Sayed Ibrahim}, Rocky Mt. J. Math. 25, No. 2, 685--699 (1995; Zbl 0832.47043) Full Text: DOI
Ibrahim, Sobhy E. Nonself-adjoint differential operators in direct sum spaces. (English) Zbl 0818.47045 Rocky Mt. J. Math. 22, No. 3, 877-915 (1992). Reviewer: H.Haruki (Waterloo / Ontario) MSC: 47E05 46B25 34B24 PDFBibTeX XMLCite \textit{S. E. Ibrahim}, Rocky Mt. J. Math. 22, No. 3, 877--915 (1992; Zbl 0818.47045) Full Text: DOI