Lemma 38.11.4. Let f : X \to S be a morphism of schemes which is flat and proper. Let U \subset S be a dense open such that X_ U \to U is finite. If also either f is locally of finite presentation or U \subset S is retrocompact, then f is finite.
Proof. By Lemma 38.11.3 the fibres of f have dimension zero. Hence f is quasi-finite (Morphisms, Lemma 29.29.5) whence has finite fibres (Morphisms, Lemma 29.20.10). Hence f is finite by More on Morphisms, Lemma 37.44.1. \square
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