  def exclude_pairs(self):
    # exclude all pairs with dist >= 4 * tolerance
    # dist_allowed is invariant under refine_adjusted_shift:
    #   exclude all pairs with dist_allowed >= tolerance
    # if 0 continuous shifts: dist_allowed == dist:
    #   exclude all pairs with dist >= tolerance
    timer = user_plus_sys_time()
    self.add_pair_ext.next_pivot(
      self.match_symmetry.continuous_shift_flags,
      self.eucl_symop,
      self.adjusted_shift,
      flex.int(self.singles1),
      flex.int(self.singles2))