1. The use of symmetry for finding the width of a partially ordered set (Russian);Alekseev;Diskret. Analiz,1974
2. A generalization of Sperner's lemma;Baker;J. Combin. Theory,1969
3. Permutation groups on unordered sets;Bercov;Math. Z,1970
4. On the set of divisors of a number;De Bruijn;Nieuw. Arch. Wisk.,1949
5. Transitivity of permutation groups on unordered sets;Cameron;Math. Z,1976