Shattered Iterations

Abstract: We develop iterated forcing constructions dual to finite support iterations in the sense that they add random reals instead of Cohen reals in limit steps. In view of useful applications we focus in particular on two-dimensional "random" iterations, which we call shattered iterations. As basic tools for such iterations we investigate several concepts that are interesting in their own right. Namely, we discuss correct diagrams, we introduce the amalgamated limit of cBa's, a construction generalizing both the direct limit and the two-step amalgamation of cBa's, we present a detailed account of cBa's carrying finitely additive strictly positive measures, and we prove a general preservation theorem for such cBa's in amalgamated limits. As application, we obtain new consistency results on cardinal invariants in Cichon's diagram. For example, we show the consistency of aleph_1 < cov (meager) < non (meager), thus answering an old question of A. Miller.