A <Sigma-1 formula> is a formula equivalent in arithmetic to $\exists y_1\cdots\exists y_r\,\delta$, where $\delta$ is bounded. A <Pi-1 formula> is similarly equivalent to $\forall y_1\cdots\forall y_r\,\delta$ with $\delta$ bounded.

Solution

Past exam of the mathematics course of the University of Cambridge / 2025 / iii / Paper 120 / 3 / a / Solution

 Solution (source code)