On logical parameterizations and functional representability in local set theories

Abstract

There is a well-known inclusion $\iota_\mathscr{E}$ of a topos $\mathscr{E}$ in the linguistic topos $\mathscr{T}(\Sigma)$ of its internal language $\Sigma$ that proves both toposes to be equivalent. There is also a canonical translation $\eta_S$ for any local set theory $S$ into the local set theory $\Sigma$ of its linguistic topos. Starting from a local set theory, this yields two a priori distinct inclusions from $\mathscr{T}(S)$ to $\mathscr{T}(\Sigma)$. Herein, these two functors are proved to be isomorphic. Furthermore, the concept of logical parameterization is investigated and then applied to see that $\iota_{\mathscr{T}(S)}$ parameterizes $\mathscr{T}(\eta_S)$ in such a way that syntactic $S$-functions are represented by themselves in $\Sigma$.