* @param tau the density threshold for the selectivity of a unit
* @return the joined unit if the selectivity of the join result is equal or
* greater than tau, null otherwise
*/
public CLIQUEUnit<V> join(CLIQUEUnit<V> other, double all, double tau) {
Interval i1 = this.intervals.last();
Interval i2 = other.intervals.last();
if(i1.getDimension() >= i2.getDimension()) {
return null;
}
Iterator<Interval> it1 = this.intervals.iterator();
Iterator<Interval> it2 = other.intervals.iterator();