The Myhill isomorphism theorem does not generalize much
Logic
2025-07-08 v1 Logic in Computer Science
Abstract
The Myhill isomorphism is a variant of the Cantor-Bernstein theorem. It states that, from two injections that reduces two subsets of to each other, there exists a bijection that preserves them. This theorem can be proven constructively. We investigate to which extent the theorem can be extended to other infinite sets other than . We show that, assuming Markov's principle, the theorem can be extended to the conatural numbers provided that we only require that bicomplemented sets are preserved by the bijection. This restriction is essential. Otherwise, the picture is overall negative: among other things, it is impossible to extend that result to either , , , , or .
Cite
@article{arxiv.2507.05028,
title = {The Myhill isomorphism theorem does not generalize much},
author = {Cécilia Pradic},
journal= {arXiv preprint arXiv:2507.05028},
year = {2025}
}
Comments
25 pages, 6 figures, draft