Tangent space to Milnor $K$-groups of rings

Abstract

We prove that the tangent space to the $(n+1)$-th Milnor $K$-group of a ring $R$ is isomorphic to group of $n$-th absolute K\"ahler differentials of $R$ when the ring $R$ contains $\frac{1}{2}$ and has sufficiently many invertible elements. More precisely, the latter condition is that $R$ is weakly $5$-fold stable in the sense of Morrow.Comment: 11 pages, to appear in Proc. Steklov Inst. Math. vol. 290 (2015