# Derived and triangulated categories

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## Abstract

A category is said to be *small* if the classes of both its objects and its morphisms are sets. A category that is not small is said to be *large*. A category ℭ is *locally small* if for any pair of objects **A** and *B* of ℭ the class Hom_{ℭ}(*A*,*B*) is a set. Many of the categories we will consider in this book (the categories of sets, groups, rings, modules over a ring, sheaves on a topological spaces, etc.) are locally small.

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## Copyright information

© Birkhäuser Boston 2009