code: @Override
  	public boolean next() {
  		if (isLhsEmpty)
  			return false;
  		if (s2.next())
  			return true;
  		else if (!(isLhsEmpty = !s1.next())) {
  			s2.beforeFirst();
  			return s2.next();
  		} else {
  			return false;
  		}
  	}
docs: Moves the scan to the next record. The method moves to the next RHS
  record, if possible. Otherwise, it moves to the next LHS record and the
  first RHS record. If there are no more LHS records, the method returns
  false.
  
  @see Scan#next()