Quotients of index two of the space of orderings of the field Q(x)


Pawel Gladki, AGH University of Science and Technology, Kraków, Poland. 29 septembre 2011 10:00 limd 2:00:00
Abstract:

Let $(X,G)$ be a space of orderings, let $G_0$ be a subgroup of index $2$ in $G$, $-1 in G_0$, and let $X_0$ denote the set of restrictions $X restriction G_0$ of elements of $X$ (viewed as characters on $G$) to characters on $G_0$. We search for necessary and sufficient conditions on $G_0$ for $(X_0,G_0)$ to be a quotient of $(X,G)$. In particular, we discuss the case when $(X,G)$ is the space of orderings of the field $Q(x)$. The talk is intended for a broad audience and all definitions necessary to follow the exposition will be explained in details. This is joint work with Murray Marshall.