... symmetries. For example, the Wilf classes for single permutations of length 4, 5, 6,and 7 are known.There are, up to symmetry, 56 classes of pairs of permutations of length four. Numer-ical data ... argument along the lines of the one above for Case 2 [Figure 12c].the electronic journal of combinatorics 12 (2005), #R25 15 Wilf classes of pairs of permutations of length 4Ian Le∗Mathematics ... permutations of length 4 are |Sn(1342, 2143)| = |Sn(3142, 2341)|and |Sn(1342, 3124)| = |Sn(1243, 2134)|, thus completing the classification of Wilf classes for pairs of permutations of length...