@article{bwmeta1.element.bwnjournal-article-fmv114i1p21bwm,
author = {Marek Wilhelm},
title = {Criteria of openness for relations},
journal = {Fundamenta Mathematicae},
volume = {112},
year = {1981},
pages = {219-228},
zbl = {0486.54010},
language = {en},
url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-fmv114i1p21bwm}
}
Wilhelm, Marek. Criteria of openness for relations. Fundamenta Mathematicae, Tome 112 (1981) pp. 219-228. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-fmv114i1p21bwm/