English

Surreal ordered exponential fields

Logic 2021-06-24 v3

Abstract

In [26], the algebraico-tree-theoretic simplicity hierarchical structure of J. H. Conway's ordered field No\mathbf{No} of surreal numbers was brought to the fore and employed to provide necessary and sufficient conditions for an ordered field (ordered KK-vector space) to be isomorphic to an initial subfield (KK-subspace) of No\mathbf{No}, i.e. a subfield (KK-subspace) of No\mathbf{No} that is an initial subtree of No\mathbf{No}. In this sequel to [15], piggybacking on the just-said results, analogous results are established for ordered exponential fields, making use of a slight generalization of Schmeling's conception of a transseries field. It is further shown that a wide range of ordered exponential fields are isomorphic to initial exponential subfields of (No,exp)(\mathbf{No}, \exp). These include all models of T(RW,ex)T(\mathbb{R}_W, e^x), where RW\mathbb{R}_W is the reals expanded by a convergent Weierstrass system WW. Of these, those we call trigonometric-exponential fields are given particular attention. It is shown that the exponential functions on the initial trigonometric-exponential subfields of No\mathbf{No}, which includes No\mathbf{No} itself, extend to canonical exponential functions on their surcomplex counterparts. The image of the canonical map of the ordered exponential field TLE\mathbb{T}^{LE} of logarithmic-exponential transseries into No\mathbf{No} is shown to be initial, as are the ordered exponential fields R((ω))EL\mathbb{R}((\omega))^{EL} and Rω\mathbb{R}\langle\langle\omega\rangle \rangle.

Keywords

Cite

@article{arxiv.2002.07739,
  title  = {Surreal ordered exponential fields},
  author = {Philip Ehrlich and Elliot Kaplan},
  journal= {arXiv preprint arXiv:2002.07739},
  year   = {2021}
}

Comments

37 pages. This version contains new material on the relationship with transseries fields, including a restatement of the main theorem (Theorem 9.1). Accepted to the Journal of Symbolic Logic