Tininess and right adjoints to exponentials

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Authors: Enrique Ruiz Hernández, Pedro Solórzano
Cited by: 0

Abstract

Objects T whose exponential functor ( − ) T admits a right adjoint ( − ) T are known under different names. The fact that they exist, yet that the only set that satisfies this in the category of sets is the singleton, made Lawvere suggest they ought to be “amazingly tiny”. In fact, he suggested to call any such object an “amazingly tiny object model” or even an “amazingly tiny objectified motion” (ATOM). This report explores how intuitively tiny any such object is. Evidences both in favor and to the contrary are produced by looking at their categorical behavior (subobjects, quotients, retracts, etc.) when the ambient category is a topos. The topological behavior (connectedness, contractibility, connected components, etc.) of both T and ( − ) T is further analyzed in toposes that satisfy certain precohesive conditions over their decidable objects, where this tininess is tested against parts of Lawvere's foundational proposal for Synthetic Differential Geometry.

Fields of Study & Subjects

Advanced Algebra and Logic Homotopy and Cohomology in Algebraic Topology Logic programming and type systems

Publication details

Journal / source
Advances in Mathematics
Volume
503
Pages
111241–111241
Publication date
11 September 2026
Language
EN