On Convergence of Filters and Ultrafilters to Subsets. - Oswald Wyler (Categorial Methods in Computer Science, 1988)

Lecture notes on Topoi and Quasitopoi. - Oswald Wyler (World Scientific, 1991)

Categories of Relations and Functional Relations. - Romaine Jayewardene; Oswald Wyler (Appl. Categorical Struct., 2000)