Equivalences and Isomorphisms
摘要
This chapter opens with the mapping cone construction. It attaches to a morphism a complex that reflects essential properties of it. The utility of this construction stretches far beyond the category of complexes, indeed, it is the key to defining a triangulated structure on the derived category. Another notion that points towards the derived category is quasi-isomorphisms; these are morphisms that induce isomorphisms in homology.