This was a talk for the Kobe Set Theory Workshop, held on the occasion of Sakaé Fuchino’s retirement, 9-11 March 2021.

Abstract. I shall discuss senses in which set-theoretic forcing can be seen as a computational process on the models of set theory. Given an oracle for the atomic or elementary diagram of a model of set theory ⟨𝑀, ∈𝑀⟩, for example, one may in various senses compute 𝑀-generic filters 𝐺 ⊂𝑃 ∈𝑀 and the corresponding forcing extensions 𝑀⁡[𝐺]. Meanwhile, no such computational process is functorial, for there must always be isomorphic alternative presentations of the same model of set theory 𝑀 that lead by the computational process to non-isomorphic forcing extensions 𝑀⁡[𝐺] ≇𝑀⁡[𝐺′]. Indeed, there is no Borel function providing generic filters that is functorial in this sense.

This is joint work with Russell Miller and Kameryn Williams.

Forcing as a computational process

[bibtex key=”HamkinsMillerWilliams:Forcing-as-a-computational-process”]