* already part of a {@link Model}. If you just created a
* {@link Rule} and didn't add it to a {@link Model} you'll
* receive a {@link NullPointerException}.
*/
public Variable getDerivedVariable() throws ModelOverdeterminedException {
OverdeterminationValidator odv = new OverdeterminationValidator(
getModel());
if (odv.isOverdetermined()) {
throw new ModelOverdeterminedException();
}
return (Variable) odv.getMatching().get(this);
}