@article{10_4153_CJM_1995_007_0,
     author = {Koppelberg, Sabine and Shelah, Saharon},
     title = {Densities of {Ultraproducts} of {Boolean} {Algebras}},
     journal = {Canadian journal of mathematics},
     pages = {132--145},
     year = {1995},
     volume = {47},
     number = {1},
     doi = {10.4153/CJM-1995-007-0},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1995-007-0/}
}