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Jun 5, 2011 at 11:36 comment added Jim Humphreys @sife: Your last question needs a more precise formulation concerning the indices of the subgroups relative to the given prime number. Like the original question asked, this further question seems too loose to answer directly.
Jun 5, 2011 at 11:32 answer added Jim Humphreys timeline score: 2
Jun 5, 2011 at 10:45 comment added sife Yes. But my question is that: if the restricted representation $V|_{H}$ is semisimple, in what conditions can we deduce that $V$ is semisimple? Here $H$ need not be a normal subgroup. Furthermore, we consider several restricted representations $\{V|_{H_{i}}\}$. If the restricted representations $\{V|_{H_{i}}\}$ are semisimple, in what conditions can we deduce that $V$ is semisimple?
Jun 5, 2011 at 8:04 comment added Niels It is probably obvious to you, but I think it is should be mentioned that the other way round, you have Clifford's theorem in modular representation theory of finite groups : Theorem (Clifford) If $H$ is any normal subgroup of $G$ and $V$ is a semi-simple $k[G]$-module, then $V_{|H}$ is a semi-simple $k[H]$-module.
Jun 5, 2011 at 6:46 history asked sife CC BY-SA 3.0