broadcast in Room 515, Cosmology Bldg., NTU, Online seminar
(線上演講 於台大次震宇宙館515教室直播/收播)
Lifting from an Ample Section The Case of Weighted Blow-ups
Marco Andreatta (Università di Torino)
Abstract:
A classical method to study a projective variety is to consider its hyperplane section and "lift" the properties of the section to the variety. This is sometimes called Apollonius method and it works well since in general a variety is at least as special as any of its hyperplane sections. For example a weighted projective space can be an hyperplane section only of a weighted projective space (S. Mori 1975).
We extend this result in a "relative situation", namely we consider

to be a local, projective, divisorial contraction between normal varieties of dimension

with

-factorial singularities and

to be a

-ample Cartier divisor. If

has a structure of a weighted blow-up then

, as well, has a structure of weighted blow-up.
As an application we consider a local projective contraction

from a variety

with terminal

-factorial singularities, which contracts a prime divisor

to an isolated

-factorial singularity

, such that \\
L)%24&chf=bg,s,333333&chco=ffffff)
is

-ample, for a

-ample Cartier divisor

on

.
Using the above result, the existence of a "good" general section of

and the existing results in dimension

, we prove that
%24&chf=bg,s,333333&chco=ffffff)
is a hyperquotient singularity and

is a weighted blow-up.
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