1. The fundamental properties of natural numbers;Grzegorz Bancerek;Formalized Mathematics,1990
2. The ordinal numbers;Grzegorz Bancerek;Formalized Mathematics,1990
3. Joining of decorated trees;Grzegorz Bancerek;Formalized Mathematics,1993
4. Segments of natural numbers and finite sequences;Grzegorz Bancerek;Formalized Mathematics,1990
5. Binary operations applied to finite sequences;Czesław Byliński;Formalized Mathematics,1990