On the Woodin Construction of Failure of GCH at a Measurable Cardinal

Abstract

Let GCH hold and let $j:V\longrightarrow M$ be a definable elementary embedding such that $crit(j)=\kappa$, $^{\kappa}M\subseteq M$ and $\kappa^{++}=\kappa_{M}^{++}$. H. Woodin proved that there is a cofinality preserving generic extension in which $\kappa$ is measurable and GCH fails at it. This is done by using an Easton support iteration of Cohen forcings for blowing the power of every inaccessible $\alpha\leq\kappa$ to $\alpha^{++}$, and then adding another forcing on top of that. We show that it is enough to use the iterated forcing, and that the latter forcing is not needed. We will show this not only for the case where $\kappa^{++}=\kappa_{M}^{++}$, but for every successor ordinal $\gamma$, where $0< \gamma< \kappa$, we will show it when the assumption is $\kappa^{+\gamma}=\kappa_{M}^{+\gamma}$.