262,466 research outputs found
Separating club-guessing principles in the presence of fat forcing axioms
We separate various weak forms of Club Guessing at in the presence of large, Martin's Axiom, and related forcing axioms. We also answer a question of Abraham and Cummings concerning the consistency of the failure of a certain polychromatic Ramsey statement together with the continuum large. All these models are generic extensions via finite support iterations with symmetric systems of structures as side conditions, possibly enhanced with -sequences of predicates, and in which the iterands are taken from a relatively small class of forcing notions. We also prove that the natural forcing for adding a large symmetric system of structures (the first member in all our iterations) adds -many reals but preserves CH
Combinatorial Properties and Dependent choice in symmetric extensions based on L\'{e}vy Collapse
We work with symmetric extensions based on L\'{e}vy Collapse and extend a few
results of Arthur Apter. We prove a conjecture of Ioanna Dimitriou from her
P.h.d. thesis. We also observe that if is a model of ZFC, then
can be preserved in the symmetric extension of in terms of
symmetric system , if
is -distributive and is -complete.
Further we observe that if is a model of ZF + , then
can be preserved in the symmetric extension of in terms of
symmetric system , if
is -strategically closed and is
-complete.Comment: Revised versio
The modal logic of forcing
What are the most general principles in set theory relating forceability and
truth? As with Solovay's celebrated analysis of provability, both this question
and its answer are naturally formulated with modal logic. We aim to do for
forceability what Solovay did for provability. A set theoretical assertion psi
is forceable or possible, if psi holds in some forcing extension, and
necessary, if psi holds in all forcing extensions. In this forcing
interpretation of modal logic, we establish that if ZFC is consistent, then the
ZFC-provable principles of forcing are exactly those in the modal theory known
as S4.2.Comment: 31 page
Iterative forcing and hyperimmunity in reverse mathematics
The separation between two theorems in reverse mathematics is usually done by
constructing a Turing ideal satisfying a theorem P and avoiding the solutions
to a fixed instance of a theorem Q. Lerman, Solomon and Towsner introduced a
forcing technique for iterating a computable non-reducibility in order to
separate theorems over omega-models. In this paper, we present a modularized
version of their framework in terms of preservation of hyperimmunity and show
that it is powerful enough to obtain the same separations results as Wang did
with his notion of preservation of definitions.Comment: 15 page
Dominating the Erdos-Moser theorem in reverse mathematics
The Erdos-Moser theorem (EM) states that every infinite tournament has an
infinite transitive subtournament. This principle plays an important role in
the understanding of the computational strength of Ramsey's theorem for pairs
(RT^2_2) by providing an alternate proof of RT^2_2 in terms of EM and the
ascending descending sequence principle (ADS). In this paper, we study the
computational weakness of EM and construct a standard model (omega-model) of
simultaneously EM, weak K\"onig's lemma and the cohesiveness principle, which
is not a model of the atomic model theorem. This separation answers a question
of Hirschfeldt, Shore and Slaman, and shows that the weakness of the
Erdos-Moser theorem goes beyond the separation of EM from ADS proven by Lerman,
Solomon and Towsner.Comment: 36 page
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