Class Field Theory
《Class Field Theory》 · 第 120–121 页 · Definition 4.35
A Postnikov system for \(X\) consists of spaces \(P_nX\) and fibrations \(p_n:P_nX\to P_{n-1}X\) with fiber \(K(\pi_n(X),n)\), such that \(\pi_m(P_nX)\cong\pi_m(X)\) for \(m\le n\) and vanishes for \(m>n\), together with compatible maps from \(X\).