Higher-dimensional forcing

Abstract

We present a method of constructing ccc forcings: Suppose first that a continuous, commutative system of complete embeddings between countable forcings indexed along ω1 is given. Then its direct limit satisfies ccc by a well-known theorem on finite support iterations. However, this limit has size at most ω1. To get larger forcings, we do not consider linear systems but higher-dimensional systems which are indexed along simplified morasses.