Algebra Seminar: Voight -- An orthogonal perspective on Gauss composition

John Voight (University of Sydney) will be speaking in the algebra seminar.  We will go
out for lunch after the talk---all are welcome to join! 

When: 12-1pm Friday August 7 

Where: Carslaw 275 

Title: An orthogonal perspective on Gauss composition 

Abstract: Classical Gauss composition relates primitive binary quadratic forms of fixed
discriminant to ideal or narrow ideal classes in the corresponding quadratic order.  We
revisit Gauss composition over a general base, exhibiting a composition law which
includes a universal version of Dirichlet composition, with a focus on orthogonal
groups.  This synthesizes work of Kneser and Wood, reconciles algebraic and geometric
approaches, and clarifies the emergence of narrow class groups.  This is joint work with
Haochen Wu.