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May 23, 2011 at 7:31 comment added Benjamin Hayes I believe the standard definition is no closed $G$-invariant subspaces.
May 21, 2011 at 16:26 answer added Andreas Thom timeline score: 2
May 15, 2011 at 3:57 comment added Yemon Choi To clarify: when you talk about an irreducible representation $\pi:G \to {\rm End}(V)$, do you mean that there is no proper $G$-invariant subspace other than zero, or do you mean that there is no proper, closed $G$-invariant subspace other than zero
May 14, 2011 at 13:24 comment added Alain Valette Mark is right. Here is for example a nice result by Michael Cowling and Tim Steger: Let $G$ be a non-compact simple Lie group, and let $\pi$ be a unitary irreducible representation of $G$; assume that $\pi$ is not in the discrete series of $G$ (you exclude countably many rep's in a continuum). Then the restriction of $\pi$ to any lattice $\Gamma$ in $G$, is an irreducible representation of $\Gamma$.
May 14, 2011 at 12:02 comment added user6976 How about the free group with two generators? Every representation of every 2-generated group is a representation of $F_2$.
May 14, 2011 at 11:39 history asked Sarah Wolfe CC BY-SA 3.0