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http://mizar.org/
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3. Bancerek, G.: The fundamental properties of natural numbers. Formalized Mathematics 1(1), 41–46 (1990)
4. Horozal, F., Kohlhase, M., Rabe, F.: Extending OpenMath with Sequences. In: Asperti, A., Davenport, J., Farmer, W., Rabe, F., Urban, J. (eds.) Intelligent Computer Mathematics, Work-in-Progress Proceedings, Volume UBLCS-2011-04 of Technical Report, University of Bologna, pp. 58–72 (2011)
5. LNAI;A. Bundy,1999