Categorical Constructions
摘要
Products and coproducts are categorical devices defined by universal properties. In the first section of this chapter, it is established that the category of R-complexes has products and coproducts. As this category is Abelian, it then follows from general principles that it has limits and colimits. In the remaining sections we give a detailed treatment of (co)limits over preordered sets, which is sufficient for our purposes.