New posts in Proof Theory

Computable extension to $Σ_1$-sound system that is $Σ_2$-unsound?

What is this property relating to logical systems called?

In mathematical induction, how does how does assuming $P(n)$ differ from assuming $\forall n : P(n)$?

Consistency of ZFC and proof by contradiction

Can every true theorem that has a proof be proven by contradiction?

Is everything provable as true, false, or undecidable?

How do we prove that something is unprovable?

Meta proof-searching

Is a proof also "evidence"?

Can proof by contradiction 'fail'?