1. Bendat, J., Sherman, S.: Monotone and convex operator functions. Trans. Amer. Math. Soc.79, 58?71 (1955)
2. Halmos, P.R.: A Hilbert space problem book. American Book 1967
3. Löwner, K.: Über monotone Matrixfunktionen. Math. Z.38, 177?216 (1934)
4. Pedersen, G.K.: Some operator monotone functions. Proc. Amer. Math. Soc.36, 309?310 (1972)
5. Stinespring, W.F.: Positive functions onC*-algebras. Proc. Amer. Math. Soc.6, 211?216 (1955)