@article{10_37236_1885,
     author = {John Dollhopf and Ian Goulden and Curtis Greene},
     title = {Words avoiding a reflexive acyclic relation},
     journal = {The electronic journal of combinatorics},
     year = {2004},
     volume = {11},
     number = {2},
     doi = {10.37236/1885},
     zbl = {1080.05003},
     url = {http://geodesic.mathdoc.fr/articles/10.37236/1885/}
}