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http://www.gutenberg.org
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4. G. Landi, An Introduction to Noncommutative Spaces and Their Geometries, Springer Lect. Notes Phys. 51, Springer Verlag (Berlin Heidelberg) (1997), [hep-th/9701078].
5. J. M. Gracia-Bondia, J. C. Varilly and H. Figueroa, Elements of Noncommutative Geometry, Birkhäuser, Boston, MA (2000).