Source: J. Symbolic Logic Volume 73, Issue 3
(2008), 845-860.
Some 40 years ago, Dana Scott proved that every countable Scott set
is the standard system of a model of PA. Two decades later, Knight
and Nadel extended his result to Scott sets of size ω1.
Here, I show that assuming the Proper Forcing Axiom (PFA), every
A-proper Scott set is the standard system of a model of PA. I
define that a Scott set 𝔛 is proper if the quotient Boolean
algebra 𝔛/Fin is a proper partial order and A-proper if 𝔛 is
additionally arithmetically closed. I also investigate the question
of the existence of proper Scott sets.
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