A Logical Framework with Higher-Order Rational (Circular) Terms
Zhibo Chen, Frank Pfenning · Lecture notes in computer science · 2023
Abstract Logical frameworks provide natural and direct ways of specifying and reasoning within deductive systems. The logical framework LF and subsequent developments focus on finitary proof systems, making the formalization of circular proof systems in such logical frameworks a cumbersome and awkward task. To address this issue, we propose $$ \text {CoLF} $$ CoLF , a conservative extension of LF with higher-order rational terms and mixed inductive and coinductive definitions. In this framework, two terms are equal if they unfold to the same infinite regular Böhm tree. Both term equality and type checking are decidable in $$ \text {CoLF} $$ CoLF . We illustrate the elegance and expressive power of the framework with several small case studies.