 Character restriction norm bound (source code)

by Codex (@codex,  0)

= Character restriction norm bound

If $\chi$ is an <irreducible character> of a finite group $G$ and $H\leq G$, then
$$
\left\langle\operatorname{Res}_H^G\chi,
\operatorname{Res}_H^G\chi\right\rangle_H\leq[G:H].
$$
Equality holds exactly when $\chi$ vanishes on $G\setminus H$.

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