anchor.diff:  
   -spec inbetween(number(), number(), number(), number(), erstar:rtree()) -> [erstar:treeleaf()].
   
  +inbetween(Phi, Lambda, FartherThan, CloserThan, RStar) when FartherThan > ?PI / 2.0, Lambda > 0.0 ->
  +    inbetween(-Phi, Lambda - ?PI, ?PI - CloserThan, ?PI - FartherThan, RStar);
  +
  +inbetween(Phi, Lambda, FartherThan, CloserThan, RStar) when FartherThan > ?PI / 2.0 ->
  +    inbetween(-Phi, Lambda + ?PI, ?PI - CloserThan, ?PI - FartherThan, RStar);
  +
   inbetween(Phi, Lambda, FartherThan, CloserThan, RStar) ->
       Extents = small_circle_extents(Phi, Lambda, CloserThan),
       erstar:walk(fun (Type, Bound) ->
  
positive.code:     distance/4
  ]).
  
  -ifdef(NIFEXT).
  
  -on_load(init/0).
  
negative.code:     end, RStar).
  
  %%
  
  %% @doc Converts degrees to radians.
  
  