© 2002 by London Mathematical Society
© The London Mathematical Society
Schemes of Line Modules I
Department of Mathematics, University of Oregon Eugene, OR 97403-1222, USA, shelton{at}math.uoregon.edu
Department of Mathematics Box 19408, University of Texas at Arlington, Arlington, TX 76019-0408, USA vancliff{at}math.uta.edu
Received 14 September 2000. Revision received 1 August 2001.
It is proved that there exists a scheme that represents the functor of line modules over a graded algebra, and it is called the line scheme of the algebra. Its properties and its relationship to the point scheme are studied. If the line scheme of a quadratic, Auslander-regular algebra of global dimension 4 has dimension 1, then it determines the defining relations of the algebra.
Moreover, the following counter-intuitive result is proved. If the zero locus of the defining relations of a quadratic (not necessarily regular) algebra on four generators with six defining relations is finite, then it determines the defining relations of the algebra. Although this result is non-commutative in nature, its proof uses only commutative theory.
The structure of the line scheme and the point scheme of a 4-dimensional regular algebra is also used to determine basic incidence relations between line modules and point modules.