Zayed, Elsayed M.E., Rahman, Hanan M.Abdel (2010)

Applied Mathematics E-Notes [electronic only]

Jaroslav Hančl (1989)

Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica

Cholewinski, Frank M., Reneke, James A. (2003)

Electronic Journal of Differential Equations (EJDE) [electronic only]

Jaroslav Hančl (1989)

Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica

Suazo, Erwin, Suslov, Sergei K., Vega-Guzmán, José M. (2011)

The New York Journal of Mathematics [electronic only]

Krupka, D. (2006)

Lobachevskii Journal of Mathematics

W. Watzlawek (1987)

Banach Center Publications