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Timeline for When is Inn(X) simple?

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Nov 22, 2010 at 23:39 comment added Jack Schmidt Thanks! That makes the situation very clear. In general Z(X)∩X′ need not be a summand of Z(X), but of course it is in the elementary abelian case.
Nov 22, 2010 at 22:18 comment added Derek Holt In that case (assuming $X$ finite of course) $Z(X)$ is a direct product of elementary abelian groups, so don't we get $Z(X) = (Z(X) \cap X') \times A$ for some $A$ and then $X = X' \times A$?
Nov 22, 2010 at 22:05 comment added Jack Schmidt If Z(X) has no elements of prime-squared order, must X' be a direct factor? It seemed like H^2(X/Z(X),p) would control it, and that it would not allow anything exciting. Maybe this also just follows by thinking about the definition of central product long enough?
Nov 22, 2010 at 20:57 history answered Derek Holt CC BY-SA 2.5