@article{tjant2017563,
author={{Callan, David and Mansour, Toufik},
title={Enumeration of 2-Wilf Classes of Four 4-letter Patterns},
journal={Turkish Journal of Analysis and Number Theory},
volume={5},
number={6},
pages={210--225},
year={2017},
url={http://pubs.sciepub.com/tjant/5/6/3},
issn={2333-1232},
abstract={Let<i> S</i><SUB><i>n</i></SUB> be the symmetric group of all permutations of <i>n</i> letters. We show that there are precisely 64 Wilf classes consisting of exactly 2 symmetry classes of subsets of four 4-letter patterns.},
doi={10.12691/tjant-5-6-3}
publisher={Science and Education Publishing}
}