1. Segments of natural numbers and finite sequences;Grzegorz Bancerek;Formalized Mathematics,1990
2. Functions and their basic properties;Czesław Byliński;Formalized Mathematics,1990
3. Functions from a set to a set;Czesław Byliński;Formalized Mathematics,1990
4. Some basic properties of sets;Czesław Byliński;Formalized Mathematics,1990
5. Finite sets;Agata Darmochwał;Formalized Mathematics,1990