@article{10_14712_1213_7243_2015_159,
     author = {Herrlich, Horst and Howard, Paul and Keremedis, Kyriakos},
     title = {On preimages of ultrafilters in {ZF}},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {241--252},
     publisher = {mathdoc},
     volume = {57},
     number = {2},
     year = {2016},
     doi = {10.14712/1213-7243.2015.159},
     mrnumber = {3513447},
     zbl = {06604504},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.14712/1213-7243.2015.159/}
}