Coherence reflected by finite direct image

ID: coherence-reflected-by-finite-direct-image

For a finite morphism between Noetherian schemes, a quasi-coherent sheaf is coherent exactly when its direct image sheaf is coherent. Over an affine target chart, let be the finite algebra over the target ring , and let represent the sheaf on . Finite generation of over implies finite generation over , using the same generators; finite generation over implies finite generation over because is finite over .

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