## All Dissertations, Theses, and Capstone Projects

#### Title

Force to change large cardinal strength

5-2015

Dissertation

Ph.D.

Mathematics

Joel D. Hamkins

Mathematics

#### Keywords

forcing; large cardinals; set theory

#### Abstract

This dissertation includes many theorems which show how to change large cardinal properties with forcing. I consider in detail the degrees of inaccessible cardinals (an analogue of the classical degrees of Mahlo cardinals) and provide new large cardinal definitions for degrees of inaccessible cardinals extending the hyper-inaccessible hierarchy. I showed that for every cardinal $\kappa$, and ordinal $\alpha$, there is a notion of forcing $\mathbb{P}$ such that $\kappa$ is still $\beta$-inaccessible in the extension, for every $\beta < \alpha$, but not $\alpha$-inaccessible. I also consider Mahlo cardinals and degrees of Mahlo cardinals. I showed that for every cardinal $\kappa$, and ordinal $\alpha$, there is a notion of forcing $\mathbb{P}$ such that for every $\beta < \alpha$, the cardinal $\kappa$ is still $\beta$-Mahlo in the extension, but not $\alpha$-Mahlo. I also show that a cardinal $\kappa$ which is Mahlo in the ground model can have every possible inaccessible degree in the forcing extension, but no longer be Mahlo there. The thesis includes a collection of results which give forcing notions which change large cardinal strength from weakly compact to weakly measurable, including some earlier work by others that fit this theme. I consider in detail measurable cardinals and Mitchell rank. I show how to change a class of measurable cardinals by forcing to an extension where all measurable cardinals above some fixed ordinal $\alpha$ have Mitchell rank below $\alpha.$ Finally, I consider supercompact cardinals, and strongly compact cardinals. I show how to change the Mitchell rank for supercompactness for a class of cardinals.

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