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by srcreigh 715 days ago
Thanks for explaining this, it truly is fascinating.

This appears to be an argument that almost every axiomatic theory isn't Σ₁-sound. So I can only ask a few things:

1. How do I even learn about Σ₁-soundness? I've tried for 30 minutes now to search for it.

2. Is my impression correct? Does this argument show that for ex ZFC is not Σ₁-sound? If not, which axiomatic theories exactly fall into this trap?