EXTENDED FRAMES AND SEPARATIONS OF LOGICAL PRINCIPLES
Makoto Fujiwara, Hajime Ishihara, Takako Nemoto, Nobu -Yuki Suzuki, Keita Yokoyama · Bulletin of Symbolic Logic · 2023
Abstract We aim at developing a systematic method of separating omniscience principles by constructing Kripke models for intuitionistic predicate logic $\mathbf {IQC}$ and first-order arithmetic $\mathbf {HA}$ from a Kripke model for intuitionistic propositional logic $\mathbf {IPC}$ . To this end, we introduce the notion of an extended frame, and show that each IPC-Kripke model generates an extended frame. By using the extended frame generated by an IPC-Kripke model, we give a separation theorem of a schema from a set of schemata in $\mathbf {IQC}$ and a separation theorem of a sentence from a set of schemata in $\mathbf {HA}$ . We see several examples which give us separations among omniscience principles.