TY  - JOUR
AU  - Marek Wilhelm
TI  - Criteria of openness for relations
JO  - Fundamenta Mathematicae
PY  - 1981
SP  - 219
EP  - 228
VL  - 114
IS  - 3
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/articles/10.4064/fm-114-3-219-228/
DO  - 10.4064/fm-114-3-219-228
LA  - en
ID  - 10_4064_fm_114_3_219_228
ER  -