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A Reflection Group of Order 168


by Steven H. Cullinane, Dec. 7, 2007


Reflection Groups: "These are groups (acting on a finite dimensional vector space) generated by reflections: elements that fix a hyperplane pointwise. They include the Weyl and Coxeter groups, complex reflection groups... and reflection groups over arbitrary fields." -- Anne V. Shepler, home page, 2007

Note that this definition includes the simple group of order 168, which is isomorphic to GL(3,2), the general linear group of three dimensions over the two-element field.

We may visualize this group as generated by reflections in the form of certain permutations of parts of the eightfold cube (below) that all fix the same (arbitrarily selected) subcube. 

The Eightfold Cube

For details, see The Fano Plane Revisualized and Binary Coordinate Systems.

There are larger easily-visualized finite reflection groups over the binary field
(and, of course, a smaller such group).  See Finite Geometry of the Square and Cube.

For reflection groups over other finite fields, see the following:

1. Linear Groups Generated by Reflection Tori (pdf), by Arjeh M. Cohen, Hans Cuypers, and Hans Sterk (Canad. J. Math. Vol. 51 (6), 1999, pp. 1149-1174).

2. From a turpion.org page for Mathematics of the USSR-- Izvestiya:

FINITE LINEAR GROUPS GENERATED BY REFLECTIONS
by A. E. Zalesskii and V. N. Serezhkin

Abstract
A complete classification is given of all finite irreducible linear groups generated by reflections over an arbitrary field of characteristic not 2.

Bibliography: 10 titles.

DOI 10.1070/IM1981v017n03ABEH001369
Citation  A E Zalesskii, V N Serezhkin, "FINITE LINEAR GROUPS GENERATED BY REFLECTIONS", MATH USSR IZV, 1981, 17 (3), 477-503.
Classification  AMS MSC: Primary: 20H15, 51F15
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