1. On the free product of associative rings;Cohn;Math. Z.,1959
2. Algebra-valued functors in general and tensor products in particular;Freyd,1966
3. Structure of categories;Isbell;Bull. Amer. Math. Soc.,1966
4. Affinity and strength in groups and related structures;Klun,1974
5. Some Algebraic Problems in the Context of Functorial Semantics of Algebraic Theories;Lawvere,1968