1. Association of Mizar Users, Library Committee. 1995, Preliminaries to structures, (Available at http://mizar.org/JFM/Addenda/struct_ 0.html)
2. Hilbert basis theorem;Backer;Formalized Math. (Available at http://mizar.org/JFM/Vol12/hilbasis.html, to appear),2000
3. Ring ideals;Backer;Formalized Math. (Available at http://mizar.org/JFM/Vol12/ideal1.html, to appear),2000
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5. Zermelo theorem and axiom of choice;Bancerek;Formalized Math. (Available at http://mizar.org/JFM/Vol1/wellord2.html.),1990