نظریه دسته‌ها [یادداشت‌های درسی]

a collection of objects, ob C; equipped with: A category is said to be small if ob C and all of the C(X, Y) are sets, and locally small if each C(X, Y) is a set. ##   If f ∈ C(X, Y), we say that X and Y are the domain (or source) and the codomain (or target) of f.  Morphisms are also referred to as maps or arrows.  We can write Hom C for the collection of all morphisms.  It is convenient and customary to assume that the C(X, Y) are disjoint for distinct pairs (X, Y).  We don't worry ourselves with the niceties of set theory.