Skip to main content
2 of 2
Brief editing of typo
Sam Sanders
  • 4.4k
  • 1
  • 21
  • 38

Comprehension axiom that helps in the opposite direction

Usually, having more comprehension axiom means the more you can prove. We wonder if the converse can be the case.

Is there a natural problem $\mathsf{P}$ so that $\mathsf{P}+\neg(\Gamma-\mathsf{ComprehensionAxiom})$ implies $\mathsf{Q}$, but $\mathsf{P}$ does not implies $\mathsf{Q}$.

Also I'd like to exclude some trivial case such as $\mathsf{Q}$ is $\neg(\Gamma-\mathsf{ComprehensionAxiom})$. We can accept $\mathsf{Q}$ to be some Comprehension Axiom, but not the negation of them. The implication is not necessary over $\mathsf{RCA}$ and $\Gamma$ can be any set of formulas.

Jiayi Liu
  • 909
  • 4
  • 10