@article{1183528620, author = {Frol\'\i k, Zden\v ek}, title = {Sums of ultrafilters}, journal = {Bull. Amer. Math. Soc.}, volume = {73}, number = {6}, year = {1967}, pages = { 87-91}, language = {en}, url = {http://dml.mathdoc.fr/item/1183528620} }
Frolík, Zdeněk. Sums of ultrafilters. Bull. Amer. Math. Soc., Tome 73 (1967) no. 6, pp. 87-91. http://gdmltest.u-ga.fr/item/1183528620/