Conservativity of ultrafilters with the P-point and Ramsey properties

Let TT be one of

ACA0,ATR0,Π11\mathcharCA0.\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=S0S1\mathbb{N}=S_0\cup S_1\cup\cdots with SnUS_n\notin\mathfrak{U} for every nn, there is an AUA\in\mathfrak{U} such that ASnA\cap S_n is finite for every nn. It is Ramsey if under the same hypothesis there is an AUA\in\mathfrak{U} such that ASn=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.

Sources & referencesView supporting material

Primary source

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

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