Skip to main content
replaced http://mathoverflow.net/ with https://mathoverflow.net/
Source Link

For a closed embedding (of varieties) $X\to Y$ let $U/X$ be etale. Is is true that there necessarily exists an etale $U'/Y$ such that $U'_X=U$? If this is wrong in general, are there any assumptions that make the statement correct ('my' $X$ is smooth, for example) or any ways to 'repair' it (in particular, I am interested in simplicial schemes).

I need this statement in order to prove my 'conjecture' Does one need to sheafify when defining the inverse image of a sheaf with respect to an embedding?Does one need to sheafify when defining the inverse image of a sheaf with respect to an embedding? The 'topological' case of my current question is trivial (for manifolds or metric spaces, at least), yet I do not understand what happens in the 'etale setting at all. Certainly, I would also be deeply grateful for any response to my previous question.:)

Upd. Now I also suspect that I need etale tubular neighbourhoods here. Yet any alternative suggestions could be very welcome!

For a closed embedding (of varieties) $X\to Y$ let $U/X$ be etale. Is is true that there necessarily exists an etale $U'/Y$ such that $U'_X=U$? If this is wrong in general, are there any assumptions that make the statement correct ('my' $X$ is smooth, for example) or any ways to 'repair' it (in particular, I am interested in simplicial schemes).

I need this statement in order to prove my 'conjecture' Does one need to sheafify when defining the inverse image of a sheaf with respect to an embedding? The 'topological' case of my current question is trivial (for manifolds or metric spaces, at least), yet I do not understand what happens in the 'etale setting at all. Certainly, I would also be deeply grateful for any response to my previous question.:)

Upd. Now I also suspect that I need etale tubular neighbourhoods here. Yet any alternative suggestions could be very welcome!

For a closed embedding (of varieties) $X\to Y$ let $U/X$ be etale. Is is true that there necessarily exists an etale $U'/Y$ such that $U'_X=U$? If this is wrong in general, are there any assumptions that make the statement correct ('my' $X$ is smooth, for example) or any ways to 'repair' it (in particular, I am interested in simplicial schemes).

I need this statement in order to prove my 'conjecture' Does one need to sheafify when defining the inverse image of a sheaf with respect to an embedding? The 'topological' case of my current question is trivial (for manifolds or metric spaces, at least), yet I do not understand what happens in the 'etale setting at all. Certainly, I would also be deeply grateful for any response to my previous question.:)

Upd. Now I also suspect that I need etale tubular neighbourhoods here. Yet any alternative suggestions could be very welcome!

added 129 characters in body; edited title
Source Link
Mikhail Bondarko
  • 16.9k
  • 4
  • 34
  • 97

Can etale $Y$$X$-schemes be lifted to $X$$Y$, where $Y$$X$ is closed in $X$$Y$?

For a closed embedding (of varieties) $X\to Y$ let $U/Y$$U/X$ be etale. Is is true that there necessarily exists an etale $U'/Y$ such that $U'_X=U$? If this is wrong in general, are there any assumptions that make the statement correct ('my' $X$ is smooth, for example) or any ways to 'repair' it (in particular, I am interested in simplicial schemes).

I need this statement in order to prove my 'conjecture' Does one need to sheafify when defining the inverse image of a sheaf with respect to an embedding? The 'topological' case of my current question is trivial (for manifolds or metric spaces, at least), yet I do not understand what happens in the 'etale setting at all. Certainly, I would also be deeply grateful for any response to my previous question.:)

Upd. Now I also suspect that I need etale tubular neighbourhoods here. Yet any alternative suggestions could be very welcome!

Can etale $Y$-schemes be lifted to $X$, where $Y$ is closed in $X$?

For a closed embedding (of varieties) $X\to Y$ let $U/Y$ be etale. Is is true that there necessarily exists an etale $U'/Y$ such that $U'_X=U$? If this is wrong in general, are there any assumptions that make the statement correct ('my' $X$ is smooth, for example) or any ways to 'repair' it (in particular, I am interested in simplicial schemes).

I need this statement in order to prove my 'conjecture' Does one need to sheafify when defining the inverse image of a sheaf with respect to an embedding? The 'topological' case of my current question is trivial (for manifolds or metric spaces, at least), yet I do not understand what happens in the 'etale setting at all. Certainly, I would also be deeply grateful for any response to my previous question.:)

Can etale $X$-schemes be lifted to $Y$, where $X$ is closed in $Y$?

For a closed embedding (of varieties) $X\to Y$ let $U/X$ be etale. Is is true that there necessarily exists an etale $U'/Y$ such that $U'_X=U$? If this is wrong in general, are there any assumptions that make the statement correct ('my' $X$ is smooth, for example) or any ways to 'repair' it (in particular, I am interested in simplicial schemes).

I need this statement in order to prove my 'conjecture' Does one need to sheafify when defining the inverse image of a sheaf with respect to an embedding? The 'topological' case of my current question is trivial (for manifolds or metric spaces, at least), yet I do not understand what happens in the 'etale setting at all. Certainly, I would also be deeply grateful for any response to my previous question.:)

Upd. Now I also suspect that I need etale tubular neighbourhoods here. Yet any alternative suggestions could be very welcome!

Source Link
Mikhail Bondarko
  • 16.9k
  • 4
  • 34
  • 97

Can etale $Y$-schemes be lifted to $X$, where $Y$ is closed in $X$?

For a closed embedding (of varieties) $X\to Y$ let $U/Y$ be etale. Is is true that there necessarily exists an etale $U'/Y$ such that $U'_X=U$? If this is wrong in general, are there any assumptions that make the statement correct ('my' $X$ is smooth, for example) or any ways to 'repair' it (in particular, I am interested in simplicial schemes).

I need this statement in order to prove my 'conjecture' Does one need to sheafify when defining the inverse image of a sheaf with respect to an embedding? The 'topological' case of my current question is trivial (for manifolds or metric spaces, at least), yet I do not understand what happens in the 'etale setting at all. Certainly, I would also be deeply grateful for any response to my previous question.:)