Past exam of the mathematics course of the University of Cambridge / 2021 / iii / Paper 129 / 2 / a / Solution

Writing $\hat{G}$ for the character group of a finite abelian group, the Bohr set with frequency set $\Gamma \subseteq \hat{G}$ and width $0\le \rho \le 2$ isIts rank is $|\Gamma |$.