1. Norm derivatives on spaces of operators;Abatzoglou;Math. Ann.,1979
2. Orthogonality in linear metric spaces;Birkhoff;Duke Math. J.,1935
3. Orthogonality of matrices and some distance problems;Bhatia;Linear Algebra Appl.,1999
4. The numerical index of the Lp space;Ed-Dari;Proc. Am. Math. Soc.,2006
5. The Toeplitz-Hausdorff theorem for linear operators;Gustafson;Proc. Am. Math. Soc.,1970