Past exam of the mathematics course of the University of Cambridge / 2018 / iii / Paper 101 / 5 / b

The unique factorization of ideals in a Dedekind domain states that every nonzero proper ideal $I$ of a Dedekind domain $D$ has a factorizationwhere the $P_j$ are distinct nonzero prime ideals and the $n_j$ are positive integers. The prime ideals and their exponents are unique up to reordering. The unit ideal $D$ is the empty product; the zero ideal is excluded.

Write $v_P(I)$ for the prime-ideal valuation in a Dedekind domain, namely the exponent of $P$ in this factorization, with zero assigned when $P$ is absent. The associated containment rule isLarger exponents give smaller ideals, just as higher divisibility gives smaller principal ideals in $\mathbb{Z}$. The theorem concerns unique factorization of ideals; it does not assert unique factorization of elements or that these ideals are principal.