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Feb 6, 2019 at 15:37 comment added LSpice @D_S, if $A$ is a non-central split torus in $C_G(g)^\circ$, then $C_G(A)$ is the Levi component of a proper ($k$-)parabolic subgroup of $G$ containing $g$.
Jan 9, 2019 at 17:08 comment added D_S But so far I don't see how we can get the converse implication.
Jan 9, 2019 at 17:06 comment added D_S Thanks for your answer. Your last paragraph seems to show just one direction: $A_G$ is a maximal split torus of $C_G^{\circ}(g)$ $\Rightarrow$ $A_G$ is the split component of $C_G^{\circ}(g)$ $\Rightarrow$ $C_G(A_G) =G$ is the unique minimal Levi containing $C_G^{\circ}(g)$. It follows that $C_G^{\circ}(g)$, hence $g$, is not a member of any proper $k$-parabolic subgroup.
S Jan 9, 2019 at 4:54 history suggested D_S CC BY-SA 4.0
Corollary 4.16 was slightly misstated
Jan 9, 2019 at 3:59 review Suggested edits
S Jan 9, 2019 at 4:54
Jan 8, 2019 at 14:11 history answered Jay Taylor CC BY-SA 4.0