}
@Override
public void explain(Deduction d, Explanation e) {
e.add(solver.getExplainer().getPropagatorActivation(this));
Variable var = d.getVar();
if (var.equals(x)) {
// a deduction has been made on x ; this is related to y only
y.explain(VariableState.DOM, e);
} else if (var != null) {
x.explain(VariableState.DOM, e);
}