1. Bell, J.L., Slomson, A.B.: Models and Ultraproducts, An Introduction. North-Holland, Amsterdam (1969)
2. Lecture Notes in Mathematics;H.A. Biagioni,1990
3. Mathematics Studies;J.-F. Colombeau,1984
4. Connes, A.: Noncommutative Geometry. Academic, New York (1994)
5. Finkelstein, D.: Past-future asymmetry of the gravitational field of a point particle. Phys. Rev. 110(4), 965–967 (1953)