1. Ando, T.: Comparison of norms $$\vert \vert \vert {f(A)-f(B)}\vert \vert \vert$$ and $$\vert \vert \vert {f({|A-B|})}\vert \vert \vert$$. Math. Z. 197, 403–409 (1988)
2. Bhatia, R.: Matrix Analysis. Springer, New York (1997)
3. Birman, M.S., Koplienko, L.S., Solomyak, M.Z.: Estimates of the spectrum of a difference of fractional powers of selfadjoint operators. Sov. Math. (Iz. VUZ) 19, 1–6 (1975)
4. Birman, M.S., Solomyak, M.Z.: Spectral Theory of Self-Adjoint Operators in Hilbert Space. D. Reidel Publishing Company, Dordrecht (1986)
5. Diestel, J., Uhl, J.J.: Vector Measures, Math. Surveys Monographs, vol. 15. American Mathematical Society, Providence (1977). (MR56:12216)