Methods of Homological Algebra
《Methods of Homological Algebra》 · 第 275 页 · Chapter IV, Section 4.3
If \(\mathcal B\) is a full additive subcategory of an abelian category, closed under extensions, and \(\mathcal E\) is the class of triples in \(\mathcal B\) exact in the ambient category, then \((\mathcal B,\mathcal E)\) is an exact category.