The Transpension Type: Technical Report

Abstract: The purpose of these notes is to give a categorical semantics for the transpension type (Nuyts and Devriese, Transpension: The Right Adjoint to the Pi-type, Accepted at LMCS, 2024), which is right adjoint to a potentially substructural dependent function type. In section 2 we discuss some prerequisites. In section 3, we define multipliers and discuss their properties. In section 4, we study how multipliers lift from base categories to presheaf categories. In section 5, we explain how typical presheaf modalities can be used in the presence of the transpension type. In section 6, we study commutation properties of prior modalities, substitution modalities and multiplier modalities.