English

Tininess and right adjoints to exponentials

Category Theory 2026-02-13 v1

Abstract

Objects TT whose exponential functor ()T(-)^T admits a right adjoint ()T(-)_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'' -- hence Lawvere's acronym ``A.T.O.M.'' 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 TT and ()T(-)_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.

Keywords

Cite

@article{arxiv.2602.12239,
  title  = {Tininess and right adjoints to exponentials},
  author = {Enrique Ruiz Hernández and Pedro Solórzano},
  journal= {arXiv preprint arXiv:2602.12239},
  year   = {2026}
}

Comments

41 pages. Key words: Tininess, amazing right adjoints, precohesion

R2 v1 2026-07-01T10:34:13.636Z