The Stacks project

Lemma 71.7.5. Let $S$ be a scheme. Let $X$ be an algebraic space over $S$. Let $f \in \Gamma (X, \mathcal{O}_ X)$. The following are equivalent:

1. $f$ is a regular section, and

2. for any $x \in X$ the image $f \in \mathcal{O}_{X, \overline{x}}$ is not a zerodivisor.

3. for any affine $U = \mathop{\mathrm{Spec}}(A)$ étale over $X$ the restriction $f|_ U$ is a nonzerodivisor of $A$, and

4. there exists a scheme $U$ and a surjective étale morphism $U \to X$ such that $f|_ U$ is a regular section of $\mathcal{O}_ U$.