Iterability for (transfinite) stacks

Abstract

We establish natural criteria under which normally iterable premice are iterable for stacks of normal trees. Let [Formula: see text] be a regular uncountable cardinal. Let [Formula: see text] and [Formula: see text] be an [Formula: see text]-sound premouse and [Formula: see text] be an [Formula: see text]-iteration strategy for [Formula: see text] (roughly, a normal [Formula: see text]-strategy). We define a natural condensation property for iteration strategies, inflation condensation. We show that if [Formula: see text] has inflation condensation then [Formula: see text] is [Formula: see text]-iterable (roughly, [Formula: see text] is iterable for length [Formula: see text] stacks of normal trees each of length [Formula: see text]), and moreover, we define a specific such strategy [Formula: see text] and a reduction of stacks via [Formula: see text] to normal trees via [Formula: see text]. If [Formula: see text] has the Dodd-Jensen property and [Formula: see text] then [Formula: see text] has inflation condensation. We also apply some of the techniques developed to prove that if [Formula: see text] has strong hull condensation (introduced independently by John Steel), and [Formula: see text] is [Formula: see text]-generic for an [Formula: see text]-cc forcing, then [Formula: see text] extends to an [Formula: see text]-strategy [Formula: see text] for [Formula: see text] with strong hull condensation, in the sense of [Formula: see text]. Moreover, this extension is unique. We deduce that if [Formula: see text] is [Formula: see text]-generic for a ccc forcing then [Formula: see text] and [Formula: see text] have the same [Formula: see text]-sound, [Formula: see text]-iterable premice which project to [Formula: see text].