Radek Honzik
Global Singularization and the Failure of SCH
Preprint series: ESI preprints
MSC:
03E35 Consistency and independence results
03E55 Large cardinals
Abstract: We say that $\kappa$ is $\mu$-hypermeasurable (or $\mu$-strong) for a cardinal
$\mu \ge \kappa^+$ if there is an embedding $j:V \embed M$ with critical point
$\kappa$ such that $H(\mu)^V$ is included in $M$ and $j(\kappa) > \mu$. Such
$j$ is called a \emph{witnessing embedding}.


Building on the results in \cite{RADEKeaston}, we will show that if $V$ satisfies
GCH and $F$ is an Easton function from the regular cardinals into cardinals satisfying some
mild restrictions, then there exists a cardinal-preserving forcing extension $V^*$
where $F$ is realised on all $V$-regular cardinals and moreover: all
$F(\kappa)$-hypermeasurable cardinals $\kappa$, where $F(\kappa) > \kappa^+$, with a
witnessing embedding $j$ such that either $j(F)(\kappa) = \kappa^+$ or
$j(F)(\kappa) \ge F(\kappa)$, are turned into singular strong limit cardinals with
cofinality $\omega$. This provides some partial information about the possible structure
of a continuum function with respect to singular cardinals with countable cofinality.


As a corollary, this shows that the continuum function on a singular strong limit
cardinal $\kappa$ of cofinality $\omega$ is virtually independent of the behaviour
of the continuum function below $\kappa$, at least for continuum functions which
are simple in that $2^\alpha \in \{\alpha^+, \alpha^{++}\}$ for every cardinal
$\alpha$ below $\kappa$ (in this case every $\kappa^{++}$-hypermeasurable cardinal
in the ground model is witnessed either by a $j$ with either $j(F)(\kappa) \ge F(\kappa)$
or $j(F)(\kappa) = \kappa^+$).


Keywords: Easton's theorem, Prikry type forcings, hypermeasurable and strong cardinals, lifting