From Euler class groups to Mennicke symbols and a monic inversion principle

Abstract

Let $R$ be a regular domain of dimension $d\geq 2$ which is essentially of finite type over an infinite perfect field $k$. We compare the Euler class group $E^d(R)$ with the van der Kallen group $Um_{d+1}(R)/E_{d+1}(R)$. In the case $2R=R$, we define a map from $E^d(R)$ to $Um_{d+1}(R)/E_{d+1}(R)$ and study it in intricate details. As application, this map enables us to carry out some interesting computations on real varieties, using some very basic arguments. The formalism required to carry out the above investigation also provides us a requisite tool to show that the monic inversion principle holds for the Euler class groups.