Event
St茅phane Lamy, Universit茅 Paul Sabatier
Wednesday, September 6, 2017 15:00to16:00
Burnside Hall
Room 920, 805 rue Sherbrooke Ouest, Montreal, QC, H3A 0B9, CA
Title: Signature morphisms on the Cremona group.
Abstract: The Cremona group is the group of birational symmetries of the plane. This is a rather huge group, which is neither finitely generated nor finite dimensional. The abelianization of the Cremona group was recently studied: over the base field C, the abelianization is trivial, but over R, the abelianization is an uncountable direct sum of Z/2. I will discuss similar results over more general fields, such as number fields or finite fields. The key is to use a natural action on a square complex, to exhibit various trees as quotients or subcomplexes, and then to apply Bass-Serre theory (joint work with Susanna Zimmermann).
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