@inproceedings{i.1987almost,
title={Almost commuting matrices and a quantitative version of the Brown-Douglas-Fillmore theorem},
author={I. David Berg, and Kenneth R. Davidson},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203315657269454},
booktitle={Acta Mathematica},
volume={166},
number={1},
pages={121-161},
year={1987},
}
I. David Berg, and Kenneth R. Davidson. Almost commuting matrices and a quantitative version of the Brown-Douglas-Fillmore theorem. 1987. Vol. 166. In Acta Mathematica. pp.121-161. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203315657269454.