@article{GDZPPN00229205X, title = {A Reduction-Principle for Infinite Formulas.}, journal = {Mathematische Annalen}, volume = {152}, year = {1963}, pages = {296-303}, zbl = {0114.24504}, url = {http://dml.mathdoc.fr/item/GDZPPN00229205X} }
ENGELER, E. A Reduction-Principle for Infinite Formulas.. Mathematische Annalen, Tome 152 (1963) pp. 296-303. http://gdmltest.u-ga.fr/item/GDZPPN00229205X/