New posts in Proof Theory

What is the point of model theory?

Is there an object such that its unique existence follows from choice axiom, while its existence cannot be proven without choice axiom?

What theory of logic or types considers the "category of propositions"?

How can you derive a formula without premises?

Is law of excluded middle necessary in this proof?

What is true about a proof system that is complete but not sound?

If something is true, can you necessarily prove it's true?

Decidability vs Completeness

Infinitely long proofs

A first order logic extended with binding terms like the familiar set descriptors $\{x:\varphi\}$