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Dec 10, 2011 at 12:06 vote accept Hugo Chapdelaine
Dec 9, 2011 at 18:50 comment added François G. Dorais (Of course, I meant the sets $((1-1/n)/2,1/2)\cup(1/2,(1+1/n)/2)$.)
Dec 9, 2011 at 18:45 comment added François G. Dorais @a-fortiori: Extend the filter generated by the sets $((1-1/n)/2,0)\cup(0,(1+1/n)/2)$ to an ultrafilter $U$. Note that that if $f \in m_U$ then $f(1/2) = 0$ by continuity, but $m_U$ is not the ideal of all functions that vanish at $1/2$ since $f(x) = x-1/2$ is not in $m_U$.
Dec 9, 2011 at 17:28 comment added user2035 Could you please indicate how to construct an ultrafilter belonging to a non-maximal prime ideal (or show its existence)?
Dec 9, 2011 at 16:33 history answered Goldstern CC BY-SA 3.0