ITERATION THEOREMS FOR SUBVERSIONS OF FORCING CLASSES

Abstract We prove various iteration theorems for forcing classes related to subproper and subcomplete forcing, introduced by Jensen. In the first part, we use revised countable support iterations, and show that 1) the class of subproper, ${}^\omega \omega $ -bounding forcing notions, 2) the class of subproper, T -preserving forcing notions (where T is a fixed Souslin tree) and 3) the class of subproper, $[T]$ -preserving forcing notions (where T is an $\omega _1$ -tree) are iterable with revised countable support. In the second part, we adopt Miyamoto’s theory of nice iterations, rather than revised countable support. We show that this approach allows us to drop a technical condition in the definitions of subcompleteness and subproperness, still resulting in forcing classes that are iterable in this way, preserve $\omega _1$ , and, in the case of subcompleteness, don’t add reals. Further, we show that the analogs of the iteration theorems proved in the first part for RCS iterations hold for nice iterations as well.