@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/