Conservativity of ultrafilters with the P-point and Ramsey properties

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Let TT be one of

ACA0,ATR0,Π11\mathchar‘−CA0.\mathbf{ACA_0},\quad \mathbf{ATR_0},\quad \mathbf{\Pi^1_1\mathchar`-CA_0}.

An ultrafilter U\mathfrak{U} is a PP-point if, for every partition N=S0∪S1∪⋯\mathbb{N}=S_0\cup S_1\cup\cdots with Sn∉US_n\notin\mathfrak{U} for every nn, there is an A∈UA\in\mathfrak{U} such that A∩SnA\cap S_n is finite for every nn. It is Ramsey if under the same hypothesis there is an A∈UA\in\mathfrak{U} such that ∣A∩Sn∣=1|A\cap S_n|=1 for every nn. P-point and Ramsey ultrafilter conservativity conjecture. For each such TT, both

T+“U is a P-point”T+\text{“$\mathfrak{U}$ is a $P$-point”}

and

T+“U is Ramsey”T+\text{“$\mathfrak{U}$ is Ramsey”}

are conservative over TT. These claims concern whether adding ultrafilters with set-theoretic properties whose existence is independent of ZFC produces no new consequences over the listed reverse-mathematical base theories. The source only says that the forcing construction may adapt to these properties and supplies no proof or counterexample.

References

Primary source

Henry Towsner, “Ultrafilters in Reverse Mathematics”, arXiv:1109.3902 (2011).

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