1. The numerical range of a pair of projections;Lenard;J. Functional Analysis,1972
2. The quantum probability calculus;Jauch;Synthese,1974
3. M. Benedicks, On Fourier transforms of functions supported on sets of finite Lebesgue measure, Royal Institute of Technology, Stockholm, preprint.
4. Two subspaces;Halmos;Trans. Amer. Math. Soc.,1969
5. Perturbation Theory for Linear Operators;Kato,1966