3 papers
math.LO2025
Semi-abelian by Design: Johnstone Algebras Unifying Implication and Division
David Forsman
Johnstone demonstrated that Heyting semilattices form a semi-abelian category via a specific triple of terms. Inspired by this work, we introduce \emph{Johnstone algebras} or J-alg…
math.CT2024
On the Multicategorical Meta-Theorem and the Completeness of Restricted Algebraic Deduction Systems
David Forsman
Eight categorical soundness and completeness theorems are established within the framework of algebraic theories. Exactly six of the eight deduction systems exhibit complete semant…
math.CT2023
Functors of Variance: Heuristic Naturality and Connection to Ends
David Forsman
The concept of a variance on a category is introduced as a two-sided strict factorization system. By employing variances, we define functors of variance in a more general setting t…