|
Given a finite dimensional Hilbert space V, a
(complex or unitary) reflection
is a linear transformation of V, of finite order,
which fixes a hyperplane pointwise.
In 1954 Shephard and Todd obtained the complete classification of finite groups generated by reflections. For the primitive groups they relied on the classification of finite groups generated by homologies, which was achieved by Blichfeldt, Mitchell, and others, 50 years before. In this talk I will outline a proof of this theorem based on the classification of embeddings between line systems, where a line system in V is a set of one-dimensional subspaces of V with prescribed angles between lines. This approach leads to the identification of the reflection groups as linear groups over finite fields. After the seminar we will take the speaker to lunch. See the Algebra Seminar web page for information about other seminars in the series. Anthony Henderson anthonyh@maths.usyd.edu.au. |