@article{10_4064_fm_77_3_289_294,
     author = {M. Zuckerman},
     title = {Natural sums of ordinals},
     journal = {Fundamenta Mathematicae},
     pages = {289--294},
     publisher = {mathdoc},
     volume = {77},
     number = {3},
     year = {1972},
     doi = {10.4064/fm-77-3-289-294},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm-77-3-289-294/}
}