[FOM] Order-types of nonstandard models

[Alasdair Urquhart]

On July 30, 2003, Harvey Friedman asked:

>Also, who is credited for analyzing the unique order type of any countable
>nonstandard model of PA?

I have a vague recollection that Skolem already noted
this as an unproved aside at the end of his 1934 paper,
which established the existence of countable nonstandard
models by a restricted ultrapower construction.

However, I don't have the paper at hand now, so I am
not quite sure.