Title:  Hasse invariants and the bad reduction
of unitary Shimura varieties, I
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Speaker: Tetsushi Ito, Kyoto Univ
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Abstract: The first part will be elementary. I will recall the definition
and the basic properties of the Hasse invariant of an elliptic
curves in characteristic p>0. Then, I will discuss its role
in the classical results of Deuring, Eichler and Igusa on
the class number of quaternion algebras. I will emphasize
how the geometry of modular curves X_0(p), which has
bad reduction at p, was used in a number theoretic problem.