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6 votes
1 answer
366 views

Breaking a morphism with generic fiber $\mathbb{F}_n$

Assume we are working over $\mathbb{C}$, and we have a projective morphism with connected fibers $f: X \rightarrow Z$ whose geometric generic fiber $X_\overline{\eta}$ is isomorphic to a Hirzebruch ...
Stefano's user avatar
  • 625
1 vote
1 answer
543 views

Infinite residue field extensions and algebraic closure of residue fields

Let $X$ be a $K$-scheme of finite type over a field $K$, let $L$ be an extension field of $K$, let $X_L := L \times_K X$, and let $p:X_L \rightarrow X$ be the projection. For each $x \in X_L$ we get ...
Georg S.'s user avatar
  • 313
4 votes
1 answer
874 views

Closed points of field extension of k-scheme under projection

I really couldn't figure out the answer to the following question: Let $X$ be a scheme of finite type over a field $k$ and let $K$ be an extension field of $k$. Let $X_K := K \times_k X$ be the base ...
Georg S.'s user avatar
  • 313
6 votes
1 answer
2k views

k rational points and base change

This could be a tricky question but could help me to better understand these very interesting things. Let $X$ be an algebraic variety over a field $k$ (in the sense of a k-scheme like in Qing Liu), $...
Srks's user avatar
  • 379
20 votes
3 answers
6k views

Closed vs Rational Points on Schemes

Background: When Ueno builds the fully faithful functor from Var/k to Sch/k he mentions that the variety $V$ can be identified with the rational points of $t(V)$ over $k$. I know how to prove this on ...
Matt's user avatar
  • 970