DECIDABILITY OF ADMISSIBILITY: ON A PROBLEM BY FRIEDMAN AND ITS SOLUTION BY RYBAKOV
Jeroen Goudsmit · Bulletin of Symbolic Logic · 2020
Abstract Rybakov (1984a) proved that the admissible rules of $\mathsf {IPC}$ are decidable. We give a proof of the same theorem, using the same core idea, but couched in the many notions that have been developed in the mean time. In particular, we illustrate how the argument can be interpreted as using refinements of the notions of exactness and extendibility.