@article{10_4064_ba63_2_2,
     author = {Arthur W. Apter},
     title = {Mixed {Levels} of {Indestructibility}},
     journal = {Bulletin of the Polish Academy of Sciences. Mathematics},
     pages = {113--122},
     publisher = {mathdoc},
     volume = {63},
     number = {2},
     year = {2015},
     doi = {10.4064/ba63-2-2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ba63-2-2/}
}