Filippov's operation and some attributes John S. Spraker, Daniel C. Biles (1994) Czechoslovak Mathematical Journal
First order linear ordinary differential equations in associative algebras. Erlebacher, Gordon, Sobczyk, Garret E. (2004) Electronic Journal of Differential Equations (EJDE) [electronic only]
Functions without residue and a bilinear differential equation Eduard Wirsing (1993) Acta Arithmetica