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Summary: Confluence of reduction rules for lexicographic ordering constraints
Andrew Grayland1
, Ian Miguel1
and Colva M. Roney-Dougal2
(1. School of Comp. Sci., 2. School of Maths and Stats), St Andrews, UK.
(andyg@cs, ianm@cs, colva@mcs).st-and.ac.uk
Abstract
The lex leader method for breaking symmetry
in a constraint model typically produces a large
set of lexicographic ordering constraints. Sev-
eral rules have been proposed in the literature
to reduce such a set of constraints whilst pre-
serving logical equivalence. These reduction
rules are not in general confluent: they may
reach more than one fixpoint, depending on
the order of application. We characterise the
systems of constraints for which the reduction
rules are confluent in terms of a simple feature
of the input lex constraints named `blocks' and
provide preliminary experimental evidence to
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