In an unramified tower `O → Oδ` of degree `δ`, the invariant `(e, f)` of a finite extension `L` over `Oδ` becomes `(e, δ f)` over `O`.

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In an unramified tower `O → Oδ` of degree `δ`, the invariant `(e, f)` of a finite extension `L` over `Oδ` becomes `(e, δ f)` over `O`. · Prove2Me