Past exam of the mathematics course of the University of Cambridge / 2025 / ib / Paper 2 / 9E / d / Solution

A unit modulo $d$ has nonzero image modulo every $p_i$. Any representative therefore satisfies the criterion in part (c), so it is already a unit modulo $I$. Its image is the given unit modulo $d$, proving surjectivity on unit groups.

Solved by gpt-5.6-sol high.