A characterization of expandability of models for ZF to models for KM
A few Remarks on n-infinite Forcing Companions
A note on a result of Buss concerning bounded theories and the collection scheme.
A note on infinite forcing.
A note on the Mac Dowell-Specker theorem
A note on Δ₁ induction and Σ₁ collection
Slaman recently proved that Σₙ collection is provable from Δₙ induction plus exponentiation, partially answering a question of Paris. We give a new version of this proof for the case n = 1, which only requires the following very weak form of exponentiation: " exists for some y sufficiently large that x is smaller than some primitive recursive function of y".
A Word on the Joint Embedding Property
Addendum to “A note on the MacDowell–Specker theorem”
An application of a reflection principle
We define a recursive theory which axiomatizes a class of models of IΔ₀ + Ω ₃ + ¬ exp all of which share two features: firstly, the set of Δ₀ definable elements of the model is majorized by the set of elements definable by Δ₀ formulae of fixed complexity; secondly, Σ₁ truth about the model is recursively reducible to the set of true Σ₁ formulae of fixed complexity.
An irrational problem
Given a topological space ⟨X,⟩ ∈ M, an elementary submodel of set theory, we define to be X ∩ M with topology generated by . Suppose is homeomorphic to the irrationals; must ? We have partial results. We also answer a question of Gruenhage by showing that if is homeomorphic to the “Long Cantor Set”, then .
An Ordering of the set of Sentences of Peano Arithmetic
Approximating the standard model of analysis
Automorphisms of models of bounded arithmetic
We establish the following model-theoretic characterization of the fragment IΔ₀ + Exp + BΣ₁ of Peano arithmetic in terms of fixed points of automorphisms of models of bounded arithmetic (the fragment IΔ₀ of Peano arithmetic with induction limited to Δ₀-formulae). Theorem A. The following two conditions are equivalent for a countable model of the language of arithmetic: (a) satisfies IΔ₀ + BΣ₁ + Exp; (b) for some nontrivial automorphism j of an end extension of that satisfies IΔ₀. Here is the...
Axioms which imply GCH
We propose some new set-theoretic axioms which imply the generalized continuum hypothesis, and we discuss some of their consequences.