Friday August 22.
Room 311.
Starting time 16:00.
Speaker: Oleg Karpenkov (Moscow--Leiden).

Title:
Lattice trigonometry.
Abstract:
In this talk we introduce a notion of lattice trigonometric functions of
lattice angles in lattice geometry and study their basic properties. We
show a necessary and sufficient condition for three angles to be the
angles of some lattice triangle in terms of lattice tangents. This
condition is a version of the Euclidean condition: three angles are the
angles of some triangle iff their sum equals Pi. The condition for lattice
angles implies a global condition for a complex projective toric surfaces
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