1. The rank+nullity theorem;Jesse Alama;Formalized Mathematics,2007
2. The vector space of subsets of a set based on symmetric difference;Jesse Alama;Formalized Mathematics,2008
3. Cardinal numbers;Grzegorz Bancerek;Formalized Mathematics,1990
4. The fundamental properties of natural numbers;Grzegorz Bancerek;Formalized Mathematics,1990
5. Segments of natural numbers and finite sequences;Grzegorz Bancerek;Formalized Mathematics,1990