@article {9833,
	title = {Quantized Hall conductance as a topological invariant},
	journal = {Physical Review B},
	year = {1985},
	pages = {3372-3377},
	doi = {10.1103/PhysRevB.31.3372},
	author = {Qian Niu and D.J. Thouless and Yong-Shi Wu}
}
