Published online by Cambridge University Press: 05 October 2020
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.