nLab higher-order logic

Idea

A higher-order logic is any logic which features higher-order predicates, which are predicates of predicates or of operations. If we think of a predicate as a function to truth values, then a higher-order predicate is a function on a power set or a function set.

Typed higher-order logic may be called higher-order type theory. Typed higher-order intuitionistic logic is often identified with the internal logic of a topos.

There are also examples of dependently typed higher-order logics. One example of a dependently typed higher-order logic is a dependent type theory with a separate type judgment, identity types, dependent sum types, dependent product types, weak function extensionality and a type of all propositions. This uses the propositions as some types interpretation of dependent type theory.

Related concepts

• logic

  • propositional logic (0th order)

  • predicate logic (1st order)

  • second-order logic

  • higher order logic

    • HOL, Isabelle
    • Girard’s System Fω (also called λω) and Coquand-Huet’s calculus of constructions are the higher-order subsystems of Barendregt's lambda-cube

  • higher-order logic as a dependent type theory

• higher-order abstract syntax

• dependent type theory

• tripos

References

• Colin Rothgang?, Florian Rabe?, Christoph Benzmüller?, Theorem Proving in Dependently-Typed Higher-Order Logic – Extended Preprint, The 29th International Conference on Automated Deduction (CADE-29), July 1-5, 2023. (arXiv:2305.15382)