TY  - JOUR
AU  - Eleftherios Tachtsis
TI  - On the Existence of Free Ultrafilters on $\omega $ and on Russell-sets in ZF
JO  - Bulletin of the Polish Academy of Sciences. Mathematics
PY  - 2015
SP  - 1
EP  - 10
VL  - 63
IS  - 1
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/articles/10.4064/ba63-1-1/
DO  - 10.4064/ba63-1-1
LA  - en
ID  - 10_4064_ba63_1_1
ER  -