TY  - JOUR
AU  - Arthur W. Apter
TI  - Indestructibility, strongness, and 
 level by level equivalence
JO  - Fundamenta Mathematicae
PY  - 2003
SP  - 45
EP  - 54
VL  - 177
IS  - 1
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/articles/10.4064/fm177-1-3/
DO  - 10.4064/fm177-1-3
LA  - en
ID  - 10_4064_fm177_1_3
ER  -