{index, middle, ring} ~
{apple, other apple, other other apple} ~
{1, 2, 3}
as representatives of the class "3" etc etc, predicates would be "don't include overripe apples when you count" etc. Then additions are unions and so on, and the Peano axioms are a consequence.[1] In my view Peano axioms are the Platonic ideal of arithmetic, after the cruft of bijections and whatnot are tossed away. I agree this is splitting hairs.
I'm wondering whether there are decidable first-order theories about the natural numbers that are stronger than either Skolem or Presburger arithmetic, that presumably use more powerful number theory. Ask "Deep Research"?
[edit] Found something without AI help: The theory of real-closed fields is decidable, PLUS the theory of p-adically closed fields is also decidable - then combined with Hasse's Principle, this might take you beyond Skolem.
[edit] Speculating about something else: Is there a decidable first-order theory of some aspects of analytic number theory, like Dirichlet series? That might also take you beyond Skolem. https://en.wikipedia.org/wiki/Analytic_number_theory#Methods...