def add_linear_constraints(self, *relations):
constraints = []<EOL>for relation in relations:<EOL><INDENT>if self._check_relation(relation):<EOL><INDENT>constraints.append(Constraint(self, None))<EOL><DEDENT>else:<EOL><INDENT>for name in self._add_constraints(relation):<EOL><INDENT>constraints.append(Constraint(self, name))<EOL><DEDENT><DEDENT><DEDENT>return constraints<EOL>
Add constraints to the problem

        Each constraint is represented by a Relation, and the
        expression in that relation can be a set expression.