Methods of Homological Algebra
《Methods of Homological Algebra》 · 第 122 页 · Chapter II, Section 6.3
For an additive category \(\mathcal A\) and full additive subcategory \(\mathcal B\), the quotient \(\mathcal A/\mathcal B\) has the same objects and morphism groups modulo morphisms factoring through objects of \(\mathcal B\).