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This article is part of the first author’s Bachelor thesis under the supervision of the second author.

Published Online: 2013-02-02Published in Print: 2012-12-01Citation Information:Formalized Mathematics. Volume 20, Issue 3, Pages 199–203, ISSN (Online) 1898-9934, ISSN (Print) 1426-2630, DOI: https://doi.org/10.2478/v10037-012-0023-z, February 2013This content is open access.