- Alberto A. Condori, “An Index Formula in Connection with Meromorphic Approximation”, Complex Anal. Oper. Theory, 7, № 6, 2013,
1787 
- L. Baratchart, F.L. Nazarov, V.V. Peller, “Analytic approximation of matrix functions in Lp”, Journal of Approximation Theory, 158, № 2, 2009,
242