Mortini, R., and R. Rupp. “Approximation by Invertible Elements and the Generalized $E$-Stable Rank for $A({\boldsymbol D})_{\mathsf R}$ and $C({\boldsymbol D})_{\mathrm{sym}}$”. MATHEMATICA SCANDINAVICA, vol. 109, no. 1, Sept. 2011, pp. 114-32, doi:10.7146/math.scand.a-15180.