English

Higman's lemma is stronger for better quasi orders

Logic 2022-05-10 v1 Combinatorics

Abstract

We prove that Higman's lemma is strictly stronger for better quasi orders than for well quasi orders, within the framework of reverse mathematics. In fact, we show a stronger result: the infinite Ramsey theorem (for tuples of all lengths) follows from the statement that any array [N]n+1Nn×X[\mathbb N]^{n+1}\to\mathbb N^n\times X for a well order XX and nNn\in\mathbb N is good, over the base theory RCA0\mathsf{RCA_0}.

Keywords

Cite

@article{arxiv.2205.04336,
  title  = {Higman's lemma is stronger for better quasi orders},
  author = {Anton Freund},
  journal= {arXiv preprint arXiv:2205.04336},
  year   = {2022}
}