• Discussing “Extended Curry-Howard Correspondence for a Basic Constructive Modal Logic”

    Discussing “Extended Curry-Howard Correspondence for a Basic Constructive Modal Logic”

    This is one of the classic papers – I’ve read, and cited, it a few times over the years myself – looking at extending the classic ‘Curry-Howard’ correspondence between lambda calculus and intuitionistic logic, to intuitionistic modal logic.

  • Discussing “Basic Proof Theory”

    Discussing “Basic Proof Theory”

    The theory of logical proofs is divided, in this well-known textbook, into two strands: structural and interpretational.

  • A Blog Update for 2025

    In the semester just finished I have been snowed under revamping and teaching a big (300+ students) introductory course on Logic. If you are interested […]

  • Discussing “Proof Analysis in Modal Logic”

    Discussing “Proof Analysis in Modal Logic”

    Modal logics of necessity and possibility do not always obviously admit an acceptable notion of structural proof theory. Yet such systems can be invaluable for both work inside the logic (proof search) and work about a logic (metatheory). This paper looks at a general framework for defining sequent calculi for a wide range of classical…

  • Discussing “An algebraic and Kripke-style approach to a certain extension of intuitionistic logic”

    Discussing “An algebraic and Kripke-style approach to a certain extension of intuitionistic logic”

    Heyting-Brouwer logic (more commonly known now as bi-intuitionistic logic) has fascinated me since I first learned of it. The idea is beguilingly simple: extend intuitionistic logic with a new connective that makes it completely symmetrical. The ‘symmetry’ I am thinking of (perhaps better called ‘duality’, but not quite the same thing as De Morgan duality)…

  • Discussing “A very modal model of a modern, major, general type system”

    Discussing “A very modal model of a modern, major, general type system”

    This paper is an influential landmark in the development of what is now usually called guarded recursion, following a trail that roughly goes from Nakano’s introduction of the approximation modality, to this paper, to a Dreyer, Ahmed, and Birkedal paper that I haven’t yet read for this blog but will probably eventually get to, to…

  • Discussing “The MetaCoq Project”

    Discussing “The MetaCoq Project”

    I’ve written before about Coq, recently renamed to Rocq, a proof assistant based on Martin-Löf’s dependent type theory. This paper, along with various sequels written in the six years since the project was first announced, aims to mechanise the syntax and semantics of Rocq, in Rocq.

  • Discussing “First Steps in Synthetic Tait Computability: The Objective Metatheory of Cubical Type Theory”

    Discussing “First Steps in Synthetic Tait Computability: The Objective Metatheory of Cubical Type Theory”

    I’ve been meaning to get more familiar with this dissertation for a while (reading it thoroughly would take longer than the week I try to take for my blog posts), after its ideas were used in a paper I discussed last year. This thesis presents a new technique, synthetic Tait computability, for proving the ‘syntactic’…

  • Discussing “Nested Sequents for Intuitionistic Logics”

    Discussing “Nested Sequents for Intuitionistic Logics”

    About a year and a half ago I wrote about hypersequents, a modification of the tried and trusted sequent calculus approach to structural proof theory. In that setting, instead of working with a single sequent (a set of premises alongside a set of possible conclusions) we work with a list of sequents. In this paper,…

  • Discussing “Modal Logic”

    Discussing “Modal Logic”

    I learned modal logic from a book by Hughes and Cresswell, a pair of philosophers from my home city of Wellington, so it was interesting for me to see the very different approach taken in this week’s book, which is now the standard reference for the field ( along with the Chargrov- Zakharyaschev book of…