# Constraint

### From Glossary

Usually this is a relation of the form of
an inequality, g(x) <= 0, or equation, h(x)=0. More generally,
it can be any restriction the decision variables must satisfy. For
example, some regard "x must be integer-valued" as a constraint,
while others would say that this is simply the domain of the
decision variables in the mathematical program. There are other
relations, such as the logical form of a precedence constraint: IF x=0 THEN y=0.

In constraint programming, a constraint is an arbitrary relation imposed on a
set of variables where each variable must be assigned on value from its domain.
A constraint *holds* if all
variables in are assigned values from their domain and the relation is satisfied.