@article{AM2_1980__20_182408,
     author = {M.J. Pelling and D.G. Rogers},
     title = {Some (2, n) combinatorial {Stein} groupoids. {(Short} {Communication).}},
     journal = {Aequationes mathematicae},
     pages = {319--320},
     year = {1980},
     volume = {20},
     zbl = {0465.20064},
     url = {http://geodesic.mathdoc.fr/item/AM2_1980__20_182408/}
}