@article{1103037137,
author = {L\'evy, A. and Vaught, R.},
title = {Principles of partial reflection in the set theories of Zermelo and Ackermann.},
journal = {Pacific J. Math.},
volume = {11},
number = {4},
year = {1961},
pages = { 1045-1062},
language = {en},
url = {http://dml.mathdoc.fr/item/1103037137}
}
Lévy, A.; Vaught, R. Principles of partial reflection in the set theories of Zermelo and Ackermann.. Pacific J. Math., Tome 11 (1961) no. 4, pp. 1045-1062. http://gdmltest.u-ga.fr/item/1103037137/