1. Barr, M., and Wells, C.: Toposes, triples and theories. Berlin, Heidelberg, New York: Springer 1984
2. Connes, A.:C * algebres et géométrie différentielle. C.R. Acad. Sc. Paris290, 599–604 (1980)
3. Research Lecture Notes in Mathematics;A. Connes,1986
4. Connes, A.: Non-commutative differential geometry. Technical Report 62, IHES, 1986
5. Connes, A.: The metric aspect of non-commutative geometry. 1991