Lemma 51.17.5. Let \varphi : A \to B be a flat ring map. If f_1, \ldots , f_ r \in A are independent, then \varphi (f_1), \ldots , \varphi (f_ r) \in B are independent.
Proof. Let I = (f_1, \ldots , f_ r) and J = \varphi (I)B. By flatness we have I/I^2 \otimes _ A B = J/J^2. Hence freeness of I/I^2 over A/I implies freeness of J/J^2 over B/J. \square
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