@article{10_37236_1922,
     author = {Ian Le},
     title = {Wilf classes of pairs of permutations of length 4},
     journal = {The electronic journal of combinatorics},
     year = {2005},
     volume = {12},
     doi = {10.37236/1922},
     zbl = {1081.05002},
     url = {http://geodesic.mathdoc.fr/articles/10.37236/1922/}
}