Abstract: I will explain what a principal homogeneous space is, and how isomorphism classes of such objects can be made into a group. Its best known incarnation is the Weil-Chatelet group in the theory of elliptic curves; in the simpler case of conics this construction is related to the class group of binary quadratic forms.

Franz Lemmermeyer (Bilkent University)

General Seminar, 1.4.2004