Tininess and right adjoints to exponentials
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