Wellfoundedness proof with the maximal distinguished set (2211.08619v1)

Abstract: In arXiv:2208.12944 it is shown that an ordinal $\sup_{N<\omega}\psi_{\Omega_{1}}(\varepsilon_{\Omega_{\mathbb{S}+N}+1})$ is an upper bound for the proof-theoretic ordinal of a set theory ${\sf KP}\ell^{r}+(M\prec_{\Sigma_{1}}V)$. In this paper we show that a second order arithmetic $\Sigma^{1-}{2}\mbox{-CA}+\Pi^{1}{1}\mbox{-CA}_{0}$ proves the wellfoundedness up to $\psi_{\Omega_{1}}(\varepsilon_{\Omega_{\mathbb{S}+N+1}})$ for each $N$. It is easy to interpret $\Sigma^{1-}{2}\mbox{-CA}+\Pi^{1}{1}\mbox{-CA}_{0}$ in ${\sf KP}\ell^{r}+(M\prec_{\Sigma_{1}}V)$.