Wong, Pui-Kei Sturmian theory of second-order elliptic differential equations and inequalities. (English) Zbl 0467.35040 J. Math. Anal. Appl. 72, 551-586 (1979). MSC: 35J15 35B05 35J60 35R45 35J20 35J65 PDF BibTeX XML Cite \textit{P.-K. Wong}, J. Math. Anal. Appl. 72, 551--586 (1979; Zbl 0467.35040) Full Text: DOI OpenURL
Kreith, Kurt Comparison theorems for special classes of nonselfadjoint elliptic equations. (English) Zbl 0281.35004 Proc. Am. Math. Soc. 42, 186-191 (1974). MSC: 35B05 35J15 35J99 PDF BibTeX XML Cite \textit{K. Kreith}, Proc. Am. Math. Soc. 42, 186--191 (1974; Zbl 0281.35004) Full Text: DOI OpenURL
Allegretto, W.; Swanson, C. A. Comparison theorems for eigenvalues. (English) Zbl 0278.35070 Ann. Mat. Pura Appl., IV. Ser. 99, 81-107 (1974). MSC: 35P15 35B05 49R50 35J15 47F05 PDF BibTeX XML Cite \textit{W. Allegretto} and \textit{C. A. Swanson}, Ann. Mat. Pura Appl. (4) 99, 81--107 (1974; Zbl 0278.35070) Full Text: DOI OpenURL
Allegretto, W. A comparison theorem for nonlinear operators. (English) Zbl 0225.35013 Ann. Sc. Norm. Super. Pisa, Sci. Fis. Mat., III. Ser. 25, 41-46 (1971). MSC: 35B05 35D99 PDF BibTeX XML Cite \textit{W. Allegretto}, Ann. Sc. Norm. Super. Pisa, Sci. Fis. Mat., III. Ser. 25, 41--46 (1971; Zbl 0225.35013) Full Text: Numdam EuDML OpenURL
Kreith, K. A comparison theorem for general elliptic equations with mixed boundary conditions. (English) Zbl 0206.11304 J. Differ. Equations 8, 537-541 (1970). MSC: 35B05 35J25 PDF BibTeX XML Cite \textit{K. Kreith}, J. Differ. Equations 8, 537--541 (1970; Zbl 0206.11304) Full Text: DOI OpenURL