@article{10_4064_cm125_1_2,
     author = {Marta Frankowska and Andrzej Nowik},
     title = {The ideal $(a)$ is not $G_\delta$ generated},
     journal = {Colloquium Mathematicum},
     pages = {7--14},
     publisher = {mathdoc},
     volume = {125},
     number = {1},
     year = {2011},
     doi = {10.4064/cm125-1-2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm125-1-2/}
}