The distance between the eigenvalues of Hermitian matrices
Rajendra Bhatia · Proceedings of the American Mathematical Society · 1986
It is shown that the minmax principle of Ky Fan leads to a quick simple derivation of a recent inequality of V. S. Sunder giving a lower bound for the spectral distance between two Hermitian matrices. This brings out a striking parallel between this result and an earlier known upper bound for the spectral distance due to L. Mirsky.