New posts in Proof Theory

Can we decide a conjecture is decidable without knowing a conjecture is correct or false?

Impossibility of certain methods of proof?

What's wrong with this inference in natural deduction?

What is the so-called eigenvariable or parameter in natural deduction?

How to prove the mathematical induction is true?

Why an inconsistent formal system can prove everything?

If all sets were finite, how could the real numbers be defined?

Are the "proofs by contradiction" weaker than other proofs?

Is there a semantics for intuitionistic logic that is meta-theoretically "self-hosting"?

Incompleteness theorems for theories with omega-rule