@article{10_4153_CJM_1966_023_2,
     author = {Hemminger, Robert L.},
     title = {On the {Group} of a {Directed} {Graph}},
     journal = {Canadian journal of mathematics},
     pages = {211--220},
     year = {1966},
     volume = {18},
     number = {1},
     doi = {10.4153/CJM-1966-023-2},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1966-023-2/}
}