anchor.diff:  type fuel_trace_status =
       | FuelTraceUnavailable
       | RecordFuelTrace of list<(int * int)>
  -    | ReplayFuelTrace of list<(int * int)>
  +    | ReplayFuelTrace of (string * list<(int * int)>)
   
   let fuel_trace : ref<fuel_trace_status> = Util.mk_ref <| FuelTraceUnavailable
   
  
positive.code:         @[Term.CheckSat]
          @suffix in
  
      let check (p:decl) =
          let cached_config =
              match !fuel_trace with 
              | ReplayFuelTrace (hd::tl) ->
                  let fuel, ifuel = hd in
                  fuel_trace := ReplayFuelTrace tl;
                  Some (fuel, ifuel)
              | _ ->
                  None
          in
          let initial_config = 
              match cached_config with 
              | Some x -> x
              | None -> (!Options.initial_fuel, !Options.initial_ifuel) 
          in
          let alt_configs = 
  
negative.code:     | Some state ->
          let digest = md5_of_file src_fn in
          if state.identity.source_digest = digest then
              fuel_trace := ReplayFuelTrace (val_fn, state.fuels)
          else
              fuel_trace := RecordFuelTrace []
      | None ->
  