@article{10_4153_CJM_2005_033_6,
     author = {Williams, Gordon},
     title = {Petrie {Schemes}},
     journal = {Canadian journal of mathematics},
     pages = {844--870},
     year = {2005},
     volume = {57},
     number = {4},
     doi = {10.4153/CJM-2005-033-6},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-2005-033-6/}
}