An Introduction to Homological Algebra
《An Introduction to Homological Algebra》 · 第 327 页 · Definition
Given a projective resolution \(P_\bullet\to A\), define \(K_0=\ker\varepsilon\) and \(K_n=\ker d_n\) for \(n\ge1\); \(K_n\) is called the \(n\)-th syzygy.