anchor.diff:  http_request_trace(State) ->
      State.
   
  +
  +%%
  +%% lens on queue head
  +qhead() ->
  +   fun(Fun, Queue) ->
  +      lens:fmap(fun(X) -> deq:poke(X, deq:tail(Queue)) end, Fun(deq:head(Queue)))      
  +   end.
  +
  
positive.code:       % http_request_trace(_),
        % http_request_enq(_),
        % http_request_log(_),
        up_link_return(Pipe, _)
     ].   
  
  
negative.code:       http_request_enq(_),
        down_link_egress(Pipe, _),
        % http_request_log(_),
        http_request_deq(_),
        down_link_return(Pipe, _)
     ].   
  
  