The Bristol Model: an abyss called a Cohen real

Asaf Karagila

Published 2017-04-23Version 1

We construct a model $M$ of ZF which lies between $L$ and $L[c]$ for a Cohen real $c$ and does not have the form $L(x)$ for any set $x$. This is loosely based on the unwritten work done in a Bristol workshop about Woodin's HOD Conjecture in 2011. The construction given here allows for a finer analysis of the needed assumptions on the ground models, thus taking us one step closer to understanding models of ZF, and the HOD Conjecture and its relatives. This model also gives a positive answer to a question of Grigorieff about intermediate models of ZF, and it can be used to show the failure of Kinna--Wagner Principles.