@article{10_4153_CJM_1970_029_8,
     author = {Bressler, D. W. and Cayford, A. H.},
     title = {Compositions of {Set} {Operations}},
     journal = {Canadian journal of mathematics},
     pages = {227--234},
     year = {1970},
     volume = {22},
     number = {2},
     doi = {10.4153/CJM-1970-029-8},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1970-029-8/}
}