Definition 29.35.1. Let $f : X \to S$ be a morphism of schemes.

We say that $f$ is

*unramified at $x \in X$*if there exists an affine open neighbourhood $\mathop{\mathrm{Spec}}(A) = U \subset X$ of $x$ and affine open $\mathop{\mathrm{Spec}}(R) = V \subset S$ with $f(U) \subset V$ such that the induced ring map $R \to A$ is unramified.We say that $f$ is

*G-unramified at $x \in X$*if there exists an affine open neighbourhood $\mathop{\mathrm{Spec}}(A) = U \subset X$ of $x$ and affine open $\mathop{\mathrm{Spec}}(R) = V \subset S$ with $f(U) \subset V$ such that the induced ring map $R \to A$ is G-unramified.We say that $f$ is

*unramified*if it is unramified at every point of $X$.We say that $f$ is

*G-unramified*if it is G-unramified at every point of $X$.

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