Extension of the Adler-Bobenko-Suris classification of integrable lattice equations
arXiv:0705.2280 · doi:10.1088/1751-8113/40/27/F03
Abstract
The classification of lattice equations that are integrable in the sense of higher-dimensional consistency is extended by allowing directed edges. We find two cases that are not transformable via the 'admissible transformations' to the lattice equations in the existing classification.
14 pages, 2 figures