@article{10_4153_CMB_1973_084_8,
     author = {Dunwoody, M. J. and Pietrowski, A.},
     title = {Presentations of the {Trefoil} {Group}},
     journal = {Canadian mathematical bulletin},
     pages = {517--520},
     year = {1973},
     volume = {16},
     number = {4},
     doi = {10.4153/CMB-1973-084-8},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1973-084-8/}
}