determinant map of k1 of a ring

Proposition

Let \(R\) be a commutative ring.
Then the determinant map of infinite general linear group

\begin{align*} \mathrm{det}(-): \mathrm{GL}(R) \rightarrow R^{\times} \end{align*}

induces an algebraic group-epimorphism

\begin{align*} K_1(R) \rightarrow R^{\times} \end{align*}

Proof - welldefined

1) independent of \(n\)

follows from Kästchensatz

2) \(E_n(R) \subseteq \mathrm{Gl}_n(R)\)

follows from

\begin{align*} \mathrm{det}(e_{i,j}(r) = 1 \end{align*}

Date: nil

Author: Anton Zakrewski

Created: 2025-01-15 Mi 17:09