ZFC + inference rules
[100 yrs old]
Halting can be thought of as a lowest term in some sequence (?)
Order relation <-> function
?? Is the Ackermann function
Paris-Harrington : not provable in PA
Proof structure :
total function [ every pair of elements has a definite ordering ]
well founded ordering
What is the simplest WL function that PA can’t prove will always terminate?
If you can’t prove halting in system X, does it mean you’re universal over system X?
Intermediate degrees: solution of Post’s problem
Computational irreducibility wrt elementary number theory....
Halting specifically is a question of computational unboundability
Computational complexity for tag system?
What do TS’s that are universal look like?