@article{GDZPPN002301792,
title = {Proper Classes as Members of Extended Sets.},
journal = {Mathematische Annalen},
volume = {180},
year = {1969},
pages = {232-240},
zbl = {0174.01703},
url = {http://dml.mathdoc.fr/item/GDZPPN002301792}
}
FRIEDMAN, J.I. Proper Classes as Members of Extended Sets.. Mathematische Annalen, Tome 180 (1969) pp. 232-240. http://gdmltest.u-ga.fr/item/GDZPPN002301792/