Wednesday, 20 April 2016

ag.algebraic geometry - A split short exact sequence of algebraic fundamental groups

If we have a variety, $X$, over a field, $k$, and $x$ is a geometric point of $X$, and let $bar x$ be a geometric point of $X_{k^s} := X times_k k^s$ above $x$ then we have the following short exact sequence:



$1 rightarrow pi_1(X_{k^s}, bar x) rightarrow pi_1(X,x) rightarrow Gal(k) rightarrow 1$



Implicit in this is a choice of $k^s$ (if you want, this is a choice of geometric point, $z$, on $Spec(k)$; $pi_1(Spec(k), z)=Gal(k)$).



I'm wondering how to interpret the splitting of this short exact sequence, and more specifically: what is the significance of choosing different splittings? I'm having a hard time picturing intuitively how to think of this splitting.

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