Ando, Linear Operators on Kreĭn Spaces, Hokkaido University, Research Institute of Applied Electricity, Division of Applied Mathematics, Sapporo, 1979.
Ando, Löwner inequality of indefinite type, Linear Algebra Appl. 385 (2004) 73--80.
Ya. Azizov and I. S. Iokhvidov, Linear Operators in Spaces with an Indefinite Metric, Nauka, Moscow, 1986, English translation: Wiley, New York, 1989.
Gohberg, P. Lancaster and L. Rodman, Indefinite linear algebra and applications, Birkhäuser Verlag, Basel, 2005.
Hassi and K. Nordström, Antitonicity of the inverse and J-contractivity, Gheondea, A. (ed.) et al., Operator extensions, interpolation of functions and related topics. 14th international conference on operator theory, Timisoara (Romania), June 1-5, 1992. Basel, Birkhäuser Verlag. Oper. Theory, Adv. Appl. 61 (1993), 149--161.
Sano, Furuta inequality of indefinite type, Math. Inequal. Appl. 10 (2007), no. 2, 381--387.
