In [1], the existence of the functor Ext in an exact category having sufficiently many
projectives and/or injectives was established. Moreover, a fairly general uniqueness …

NAB<.:(A x B) x c----f*-I;.(B% C), r, 4:= 3 x I---+--I, lA: 1<.-1-*.+ J. and k,,:-4, q B--+ B '*.-I,
colzerml in the sense of Mac I, anc [28]. Also, there exists a natural isomorphism w …

In recent years, there has been considerable discussion as to the appropriate definition of
distributive categories. Three definitions which have had some support are:(1) A category …

1. I. 77~ mnMumus functor pmblem. By a cydinder in a category C we mean a~ mdkategofy
K, two functarsP, Q: K+ C, and a natural transformation o: P-+ Q; we denote the cylinder for …

Introduction This paper is concerned with relations in general categories. MacLane [1],
Puppe [2], Hilton [3] considered the abelian case; namely, the categories of relations …

In their paper on a" General theory of natural equivalences" Eilenberg and MacLane laid the
foundation of the theory of categories and functors in 1945. It took about ten years before the …

Oberst [15], Laudal [8], Watts [20] and Andr6 [1] have shown that derived functors of colimit
define a homology theory for Rat, the category of small categories. In this paper, we show …

ordinary category would be the category of Y-functors from! to and V-natural transformations
between them. We present here some observations on the problem. The remarks in the …

The notion of derived functors is well-established as being a powerful and profound tool in
diverse areas of mathematics. The theme of CARTANEILENBERG [1] is that almost all …

1. Introduction. In a category (€, an object Q will be said to be injective with respect to a
morphism/: A-> B if for every (¡): A-+ Q there exists\¡/: B^ Q such that</>=\¡/f. An injective …