Methods of Homological Algebra
《Methods of Homological Algebra》 · 第 25 页 · Chapter I, Section 4.3
A chain complex is a sequence \(\cdots\to C_n\xrightarrow{d_n}C_{n-1}\to\cdots\) with \(d_n\circ d_{n+1}=0\) for every \(n\).