1. Exact categories and categories of sheaves;Barr,1971
2. Heterogeneous algebras;Birkhoff;J. Combin. Theory,1970
3. Ordered categories with involution;Calenko;Dissertationes Matematicae (=Rozprawy Matematyczne),1984
4. A categorical approach to realizability and polymorphic types;Carboni,1988
5. Some remarks on Maltsev and Goursat categories;Carboni;Appl. Categorical Struct.,1993