Degree of a self-map of a sphere via homology

Remark 3.3.16 (Degree). For every \(n\geq 1\), a map \(f\colon S^n\to S^n\) induces multiplication by a unique integer on \(H_n(S^n)\cong \Z \). This integer is called the degree of \(f\). For pointed maps, this agrees with the degree recorded in Remark 2.4.20.