Topology and Geometry
《Topology and Geometry》 · 第 423 页 · Section VI.17
For a closed manifold \(N^n\), there is a unique class \(v_i\in H^i(N;\mathbb Z_2)\) such that \(\langle\operatorname{Sq}^i(u),[N]\rangle=\langle v_i\smile u,[N]\rangle\) for all \(u\in H^{n-i}(N;\mathbb Z_2)\); the classes \(v_i\) are called Wu classes.