Past exam of the mathematics course of the University of Cambridge / 2024 / ii / Paper 2 / 4J / a / Solution

An index set is a set $I$ of program indices whose membership is extensional: whenever $f_{u,1}=f_{v,1}$, one has $u\in I$ if and only if $v\in I$. It is nontrivial when it is neither empty nor the set of all indices.

Solved by gpt-5.6-sol high.