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Let $f: X \to Y$ be a finite, surjective morphism of smooth, projective, irreducible varieties over $\mathbb{C}$ and let $y \in Y$.

  1. Can I find a smooth curve $C \subseteq Y$ with $y \in C$ such that $f^{-1}(C)$ is again a smooth curve?

  2. If not, can I find a curve $C \subseteq Y$ such that $y$ is a smooth point of $C$ and such that every $x \in f^{-1}(\{y\})$ is a smooth point of $f^{-1}(C)$?

  3. Can I find a curve $C \subseteq Y$ with the property of 1. or 2. with the additional property that $f$ is unramified along a Zariski dense subset of $f^{-1}(C)$?

Edit: As Yusuf recommended, I'd like to point out that I am especially interested in the case where $y$ lies in the branch locus. Also $y$ is not necessarily a smooth point of the underlying reduced scheme of the branch divisor.

Let $f: X \to Y$ be a finite, surjective morphism of smooth, projective, irreducible varieties over $\mathbb{C}$ and let $y \in Y$.

  1. Can I find a smooth curve $C \subseteq Y$ with $y \in C$ such that $f^{-1}(C)$ is again a smooth curve?

  2. If not, can I find a curve $C \subseteq Y$ such that $y$ is a smooth point of $C$ and such that every $x \in f^{-1}(\{y\})$ is a smooth point of $f^{-1}(C)$?

  3. Can I find a curve $C \subseteq Y$ with the property of 1. or 2. with the additional property that $f$ is unramified along a Zariski dense subset of $f^{-1}(C)$?

Edit: As Yusuf recommended, I'd like to point out that I am especially interested in the case where $y$ lies in the branch locus.

Let $f: X \to Y$ be a finite, surjective morphism of smooth, projective, irreducible varieties over $\mathbb{C}$ and let $y \in Y$.

  1. Can I find a smooth curve $C \subseteq Y$ with $y \in C$ such that $f^{-1}(C)$ is again a smooth curve?

  2. If not, can I find a curve $C \subseteq Y$ such that $y$ is a smooth point of $C$ and such that every $x \in f^{-1}(\{y\})$ is a smooth point of $f^{-1}(C)$?

  3. Can I find a curve $C \subseteq Y$ with the property of 1. or 2. with the additional property that $f$ is unramified along a Zariski dense subset of $f^{-1}(C)$?

Edit: As Yusuf recommended, I'd like to point out that I am especially interested in the case where $y$ lies in the branch locus. Also $y$ is not necessarily a smooth point of the underlying reduced scheme of the branch divisor.

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Hans
  • 3k
  • 13
  • 17

Let $f: X \to Y$ be a finite, surjective morphism of smooth, projective, irreducible varieties over $\mathbb{C}$ and let $y \in Y$.

  1. Can I find a smooth curve $C \subseteq Y$ with $y \in C$ such that $f^{-1}(C)$ is again a smooth curve?

  2. If not, can I find a curve $C \subseteq Y$ such that $y$ is a smooth point of $C$ and such that every $x \in f^{-1}(\{y\})$ is a smooth point of $f^{-1}(C)$?

  3. Can I find a curve $C \subseteq Y$ with the property of 1. or 2. with the additional property that $f$ is unramified along a Zariski dense subset of $f^{-1}(C)$?

Edit: As Yusuf recommended, I'd like to point out that I am especially interested in the case where $y$ lies in the branch locus.

Let $f: X \to Y$ be a finite, surjective morphism of smooth, projective, irreducible varieties over $\mathbb{C}$ and let $y \in Y$.

  1. Can I find a smooth curve $C \subseteq Y$ with $y \in C$ such that $f^{-1}(C)$ is again a smooth curve?

  2. If not, can I find a curve $C \subseteq Y$ such that $y$ is a smooth point of $C$ and such that every $x \in f^{-1}(\{y\})$ is a smooth point of $f^{-1}(C)$?

  3. Can I find a curve $C \subseteq Y$ with the property of 1. or 2. with the additional property that $f$ is unramified along a Zariski dense subset of $f^{-1}(C)$?

Let $f: X \to Y$ be a finite, surjective morphism of smooth, projective, irreducible varieties over $\mathbb{C}$ and let $y \in Y$.

  1. Can I find a smooth curve $C \subseteq Y$ with $y \in C$ such that $f^{-1}(C)$ is again a smooth curve?

  2. If not, can I find a curve $C \subseteq Y$ such that $y$ is a smooth point of $C$ and such that every $x \in f^{-1}(\{y\})$ is a smooth point of $f^{-1}(C)$?

  3. Can I find a curve $C \subseteq Y$ with the property of 1. or 2. with the additional property that $f$ is unramified along a Zariski dense subset of $f^{-1}(C)$?

Edit: As Yusuf recommended, I'd like to point out that I am especially interested in the case where $y$ lies in the branch locus.

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Hans
  • 3k
  • 13
  • 17

Preimage of smooth curves under morphism of smooth varieties

Let $f: X \to Y$ be a finite, surjective morphism of smooth, projective, irreducible varieties over $\mathbb{C}$ and let $y \in Y$.

  1. Can I find a smooth curve $C \subseteq Y$ with $y \in C$ such that $f^{-1}(C)$ is again a smooth curve?

  2. If not, can I find a curve $C \subseteq Y$ such that $y$ is a smooth point of $C$ and such that every $x \in f^{-1}(\{y\})$ is a smooth point of $f^{-1}(C)$?

  3. Can I find a curve $C \subseteq Y$ with the property of 1. or 2. with the additional property that $f$ is unramified along a Zariski dense subset of $f^{-1}(C)$?