anchor.diff:  
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   
  --spec prop_quadrant_intervals() -> true.
  -prop_quadrant_intervals() ->
  +check_quadrant_intervals(_) ->
       Quadrants = rr_recon:quadrant_intervals(),
       ?equals(lists:foldl(fun intervals:union/2, intervals:empty(), Quadrants),
               intervals:all()),
  
positive.code:     [
       {basic,  [parallel], [
                             get_symmetric_keys_test,
                             tester_quadrant_intervals,
                             tester_map_key_to_interval,
                             tester_map_key_to_quadrant,
                             tester_map_interval,
  
negative.code:                          Q1 =/= Q2,
                           not intervals:is_empty(intervals:intersection(Q1, Q2))],
              []).
  
  -spec prop_map_key_to_interval(?RT:key(), intervals:interval()) -> boolean().
  prop_map_key_to_interval(Key, I) ->
  