Remark 49.16.2. Let $f : Y \to X$ be a quasi-finite Gorenstein morphism of Noetherian schemes. Let $\mathfrak D_ f \subset \mathcal{O}_ Y$ be the different and let $R \subset Y$ be the closed subscheme cut out by $\mathfrak D_ f$. Then we have

$\mathfrak D_ f$ is a locally principal ideal,

$R$ is a locally principal closed subscheme,

$\mathfrak D_ f$ is affine locally the same as the Noether different,

formation of $R$ commutes with base change,

if $f$ is finite, then the norm of $R$ is the discriminant of $f$, and

if $f$ is étale in the associated points of $Y$, then $R$ is an effective Cartier divisor and $\omega _{Y/X} = \mathcal{O}_ Y(R)$.

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