@article{DMTCS_2017_19_1_a6,
     author = {Callan, David and Mansour, Toufik and Shattuck, Mark},
     title = {Wilf classification of triples of 4-letter patterns {I}},
     journal = {Discrete mathematics & theoretical computer science},
     publisher = {mathdoc},
     volume = {19},
     number = {1},
     year = {2017-2018},
     doi = {10.23638/DMTCS-19-1-5},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.23638/DMTCS-19-1-5/}
}