1. R/Z index theory;Lott;Comm. Anal. Geom.,1994
2. Dirac charge quantization and generalized differential cohomology;Freed,2000
3. Quadratic functions in geometry, topology, and M-theory;Hopkins;J. Differential Geom.,2005
4. U. Bunke, T. Schick, Smooth K-theory, preprint. arXiv:0707.0046
5. D-branes and K-theory;Witten;J. High Energy Phys.,1998