in the answer to this post there was the statement that a representation $\vartheta$ of a subgroup $\langle z\rangle$ can extend to a representation of the whole group $D_{2n}$.
If I start the other way round, this would mean that if the induced representation $\operatorname{Ind}(\vartheta)$ decomposes into two irreducibles $\vartheta_1$ and $\vartheta_2$,
- $\vartheta_1$ and $\vartheta_2$ have the same degree (Why can't $\operatorname{Ind}(\vartheta)$ decompose into $2$ representation with different degrees?)
- $\vartheta_1$ is the same representations as $\vartheta_2$. ( Why can't they be different?)
\langle z \rangle
to get $\langle z \rangle$. – amWhy Apr 20 '13 at 18:59