CLP[2]

Constraint Logic Programming

A programming framework based (as Prolog) on LUSH (or SLD) resolution, but in which unification has been replaced by a constraint solver. A CLP interpreter contains a Prolog-like inference engine and an incremental constraint solver. The engine sends constraints to the solver one at a time. If the new constraint is consistent with the collected constraints it will be added to the set. If it was inconsistent, it will cause the engine to backtrack.

"Constraint Logic Programming", Joxan Jaffar et al, Conference Record of the 14th Annual ACM Symposium on Principles of Programming Languages, ACM 1987.