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Dec 1, 2010 at 9:36 comment added BCnrd Dear Pete: Yes, it was a small goof. But just move on: when rank-2 is too small, a standard device is to use the rank-3 cases to handle everything else. That is why (in my various comments) I keep suggesting to look into those basic rank-3 cases, which would then handle everything else split and simply connected by using Bruhat decomposition, torus centralizers, and the like (as Jim says).
Nov 30, 2010 at 23:08 history edited Jim Humphreys CC BY-SA 2.5
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Nov 30, 2010 at 23:03 history edited Jim Humphreys CC BY-SA 2.5
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Nov 30, 2010 at 19:52 history edited Jim Humphreys CC BY-SA 2.5
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Nov 30, 2010 at 17:04 history edited Jim Humphreys CC BY-SA 2.5
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Nov 30, 2010 at 13:11 comment added Pete L. Clark @BCnrd: not yet, no. My point is that I find the sentence "On the other hand, $SL_2$ is almost simple, while its subgroup generated by involutions is obviously normal and too big to be the center" to be confusing. (Or, less politely but more plainly, it seems not to be true.)
Nov 30, 2010 at 4:08 comment added BCnrd Dear Pete: sure, but one can get at all split simply connected examples other than ${\rm{SL}}_2$ by using the rank-3 cases (SL$_3$, G$_2$, and Sp$_4$), so have you looked into those basic building blocks instead?
Nov 30, 2010 at 0:09 comment added Pete L. Clark I'm confused: as in the above comments, isn't $-1$ the only involution in $\operatorname{SL}_2$?
Nov 29, 2010 at 21:46 history edited Jim Humphreys CC BY-SA 2.5
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Nov 29, 2010 at 19:03 history edited Jim Humphreys CC BY-SA 2.5
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Nov 29, 2010 at 18:58 history answered Jim Humphreys CC BY-SA 2.5