Algebraic Topology
《Algebraic Topology》 · 第 489 页 · Section 4.L
The Steenrod square \(\operatorname{Sq}^i:H^n(X;\mathbb Z_2)\to H^{n+i}(X;\mathbb Z_2)\) is natural and additive, satisfies the Cartan formula, and has \(\operatorname{Sq}^i(\alpha)=\alpha^2\) for \(i=|\alpha|\) and zero for \(i>|\alpha|\).