@article{10_4064_fm177_1_3,
     author = {Arthur W. Apter},
     title = {Indestructibility, strongness, and 
 level by level equivalence},
     journal = {Fundamenta Mathematicae},
     pages = {45--54},
     publisher = {mathdoc},
     volume = {177},
     number = {1},
     year = {2003},
     doi = {10.4064/fm177-1-3},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm177-1-3/}
}