Lemma 72.5.3. Let S be a scheme. Let X, Y, Z be integral algebraic spaces over S. Let f : X \to Y and g : Y \to Z be dominant morphisms locally of finite type. Assume any of the equivalent conditions (1) – (5) of Lemma 72.5.1 hold for f and g. Then
\deg (X/Z) = \deg (X/Y) \deg (Y/Z).
Proof. This comes from the multiplicativity of degrees in towers of finite extensions of fields, see Fields, Lemma 9.7.7. \square
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