@article{10_21136_CMJ_1979_101618,
     author = {Levitz, Hilbert},
     title = {The {Cartesian} product of sets and the {Hessenberg} natural product of ordinals},
     journal = {Czechoslovak Mathematical Journal},
     pages = {353--358},
     publisher = {mathdoc},
     volume = {29},
     number = {3},
     year = {1979},
     doi = {10.21136/CMJ.1979.101618},
     mrnumber = {536062},
     zbl = {0426.04002},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1979.101618/}
}