@article{10_4064_fm_114_2_113_118,
     author = {Andrzej Pelc},
     title = {Solution of a problem of {Ulam} on countable sequences of sets},
     journal = {Fundamenta Mathematicae},
     pages = {113--118},
     publisher = {mathdoc},
     volume = {114},
     number = {2},
     year = {1981},
     doi = {10.4064/fm-114-2-113-118},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm-114-2-113-118/}
}