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GENERIC CODING WITH HELP AND AMALGAMATION FAILURE
Published online by Cambridge University Press: 05 October 2020
Abstract
We show that if M is a countable transitive model of
$\text {ZF}$
and if
$a,b$
are reals not in M, then there is a G generic over M such that
$b \in L[a,G]$
. We then present several applications such as the following: if J is any countable transitive model of
$\text {ZFC}$
and
$M \not \subseteq J$
is another countable transitive model of
$\text {ZFC}$
of the same ordinal height
$\alpha $
, then there is a forcing extension N of J such that
$M \cup N$
is not included in any transitive model of
$\text {ZFC}$
of height
$\alpha $
. Also, assuming
$0^{\#}$
exists, letting S be the set of reals generic over L, although S is disjoint from the Turing cone above
$0^{\#}$
, we have that for any non-constructible real a,
$\{ a \oplus s : s \in S \}$
is cofinal in the Turing degrees.
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- © Association for Symbolic Logic 2020
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