Timeline for Sections and subgroups in a unipotent group
Current License: CC BY-SA 2.5
2 events
| when toggle format | what | by | license | comment | |
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| Jul 8, 2010 at 3:07 | comment | added | BCnrd | Nice! Via gp Ex($V$, $W$) of central ex'tns, you pull back Witt class in Ex($\mathbf{G}_ a$, $\mathbf{G}_ a$) along $\phi:V \rightarrow \mathbf{G}_ a$ in 1st variable to get class in Ex($V$, $\mathbf{G}_ a$), which you add to class defined by $\beta$ to get the central ext'n $E_1$. To get non-commutativity (so $[E_1, E_1]$ as expected), need $\beta$ non-symmetric rather than alt'ing, so take $p > 2$ and $\beta \ne 0$. To get $\pi^{-1}(L) = W_2$ as central ext'n want $\beta$ alternating, but full force of non-degeneracy isn't needed. Anyway, let's see what Harald has to say. | |
| Jul 7, 2010 at 13:43 | history | answered | George McNinch | CC BY-SA 2.5 |