@article{10_4153_CJM_1976_086_7,
     author = {Zorzitto, Frank},
     title = {Purity {And} {Copurity} in {Systems} of {Linear} {Transformations}},
     journal = {Canadian journal of mathematics},
     pages = {889--896},
     year = {1976},
     volume = {28},
     number = {4},
     doi = {10.4153/CJM-1976-086-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1976-086-7/}
}