1. Ansorg M., Pfister H.: A universal constraint between charge and rotation rate for degenerate black holes surrounded by matter. Class. Quantum Grav. 25, 035009 (2008)
2. Bardeen, J.M.: Rapidly rotating stars, disks, and black holes. In: Black holes (Les Houches), deWitt, C., deWitt, B.S., ed., London: Gordon and Breach, 1973, pp. 241–289
3. Booth I., Fairhurst S.: Extremality conditions for isolated and dynamical horizons. Phys. Rev. D 77, 084005 (2008)
4. Buttazzo G., Giaquinta M., Hildebrandt S.: One-dimensional variational problems. Clarendon Press, Oxford (1998)
5. Carter, B.: Black hole equilibrium states. In: Black Holes (Les Houches), deWitt, C., deWitt, B.S., ed., London: Gordon and Breach, 1973, pp. 57–214