}
@Override
public TruthValue contains(Expression element) {
if (element instanceof ANumber) {
Expression leftTest = leftClosed ? new LE(a, element).evaluate() : new LT(a, element).evaluate();
Expression rightTest = rightClosed ? new LE(element, b).evaluate() : new LT(element, b).evaluate();
if (leftTest instanceof TruthValue && rightTest instanceof TruthValue) {
return ((TruthValue) leftTest).and((TruthValue) rightTest);
}
}