English

An elementary description of $K_1(R)$ without elementary matrices

K-Theory and Homology 2019-10-11 v2

Abstract

Let RR be a ring with unit. Passing to the colimit with respect to the standard inclusions GL(n,R)GL(n+1,R)GL(n,R) \to GL(n+1,R) (which add a unit vector as new last row and column) yields, by definition, the stable linear group GL(R)GL(R); the same result is obtained, up to isomorphism, when using the "opposite" inclusions (which add a unit vector as new first row and column). In this note it is shown that passing to the colimit along both these families of inclusions simultaneously recovers the algebraic KK-group K1(R)=GL(R)/E(R)K_1(R) = GL(R)/E(R) of~RR, giving an elementary description that does not involve elementary matrices explicitly.

Keywords

Cite

@article{arxiv.1910.02771,
  title  = {An elementary description of $K_1(R)$ without elementary matrices},
  author = {Thomas Huettemann and Zuhong Zhang},
  journal= {arXiv preprint arXiv:1910.02771},
  year   = {2019}
}

Comments

2 pages; v2: two variations of result discussed

R2 v1 2026-06-23T11:36:21.389Z