%0 Journal Article
%A Eleftherios Tachtsis
%T On the Existence of Free Ultrafilters on $\omega $ and on Russell-sets in ZF
%J Bulletin of the Polish Academy of Sciences. Mathematics
%D 2015
%P 1-10
%V 63
%N 1
%I mathdoc
%U http://geodesic.mathdoc.fr/articles/10.4064/ba63-1-1/
%R 10.4064/ba63-1-1
%G en
%F 10_4064_ba63_1_1