@article{10_4153_CJM_1977_073_4,
     author = {Okoh, Frank},
     title = {Systems that are {Purely} {Simple} and {Pure} {Injegtive}},
     journal = {Canadian journal of mathematics},
     pages = {696--700},
     year = {1977},
     volume = {29},
     number = {4},
     doi = {10.4153/CJM-1977-073-4},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1977-073-4/}
}