On $\omega_3$-chains in P($\omega_1$) mod finite

Abstract

We prove that if there exists a simplified $(\omega_1,2)$-morass, then there is a ccc forcing which adds an $\omega_3$-chain in P($\omega_1$) mod finite and a ccc forcing which adds a family of $\omega_3$-many strongly almost disjoint functions from $\omega_1$ to $\omega$. The idea is to use a finite support iteration of countable forcings which is not linear but three-dimensional.