Brody, D C and Hughston, L P. 1998. Geometric Models for Quantum Statistical Inference. In: S A Huggett; L J Mason; K P Tod and S T Tsou, eds. The Geometric Universe: Science, Geometry, and the Work of Roger Penrose. Oxford: Oxford University Press, pp. 265-276. ISBN 0198500599 [Book Section]

Hughston, L P and Tod, K P. 1990. An Introduction to General Relativity. Cambridge: Cambridge University Press. ISBN 0521327059 [Book]