@article{10_4153_CJM_1971_001_1,
     author = {Gorman, Howard},
     title = {Invertibility and {Class} {Number} of {Orders}},
     journal = {Canadian journal of mathematics},
     pages = {1--11},
     year = {1971},
     volume = {23},
     number = {1},
     doi = {10.4153/CJM-1971-001-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1971-001-1/}
}