Graduate Clarification of Mihăilescu's Theorem (Catalan's Conjecture)

[e2m2a]

TL;DR

I understand Catalan's conjecture was proven by Preda V. Mihăilescu in 2002. However, I am not sure if it is proved for only certain conditions.

Mihăilescu's theorem proves that Catalan's conjecture is true. That is for x^a - y^b = 1, the only possible solution in naturual numbers for this equation is x=3, a=2, y=2, b=3. What is not clear to me is this. Does Mihăilescu's theorem prove that the difference between any other two powers (not the Catalan expression) will never be equal to 1 but only within certain restrictions? Another words, are there conditions that restrict x or y have to be both prime integers or just one of them must be a prime integer or does a or b have to be both prime integers or just one of them must be a prime integer for Mihăilescu's theorem to be true? Or is the only condition necessary is that x,y >0 and a.b >1?

 

[Office_Shredder]

I think Wikipedia accurately describes the restrictions

https://en.m.wikipedia.org/wiki/Catalan's_conjecture