anchor.diff:  %%% External interface functions
   %%%------------------------------------------------------------------------
   
  +-ifdef(ERLANG_OTP_VER_16).
   -type pqueue4() ::
       {integer() | 'empty', % current priority
        integer(),           % total size
  
positive.code:       queue(), queue(), queue(), queue(), queue(), queue(), queue(), queue()},
       {queue(), queue(), queue(), queue(), queue(), queue(), queue(), queue(),
        queue(), queue(), queue(), queue(), queue(), queue(), queue(), queue()}}.
  
  %%-------------------------------------------------------------------------
  %% @doc
  
negative.code: %% (based on the implementation of queue:filter/2 which is under the EPL)
  %%-------------------------------------------------------------------------
  
  -ifdef(ERLANG_OTP_VER_16).
  -spec queue_remove_unique(F :: fun((any()) -> boolean()),
                            queue()) ->
      {boolean(), queue()}.
  -else.
  -spec queue_remove_unique(F :: fun((any()) -> boolean()),
                            queue:queue()) ->
      {boolean(), queue:queue()}.
  -endif.
  queue_remove_unique(Fun, {R0, F0} = Q)
      when is_function(Fun, 1), is_list(R0), is_list(F0) ->
      case queue_remove_unique_f(Fun, F0) of
  