On Lawrence semigroups
Lawrence semigroups arise as a tool to compute Graver bases of semigroup ideals. It is known that the minimal free resolution of semigroup ideals is characterized by the reduced homologies of certain simplicial complexes. In this paper we study the minimal degrees of a Lawrence semigroup ideal and its first syzygy given a combinatorial characterization of the nonvanishing cycles in their associated reduced homologies. We specialize the results that appeared in [Briales, E., Campillo, A., Marijuan, C., Pison, P., 1998. Minimal systems of generators for ideals of semigroups. J. Pure Appl. Algebra, 127, 7-30] and [Pison-Casares, P., Vigneron-Tenorio, A., 2001. First syzygies of toric varieties and diophantine equations in congruence. Comm. Alg. 29 (4), 1445-1466] to the Lawrence semigroups. (C) 2008 Elsevier Ltd. All rights reserved.
semigroup ideal simplicial complex graver basis grobner basis lattice ideal lawrence lifting