Fang, Junsheng, Don Hadwin, and Xiujuan Ma. “On Spectra and Brown’s Spectral Measures of Elements in Free Products of Matrix Algebras”. MATHEMATICA SCANDINAVICA 103, no. 1 (September 1, 2008): 77–96. Accessed May 3, 2024. https://www.mscand.dk/article/view/15070.