anchor.diff:                         {ok, V2s} = orddict:find(LPN, Values),
                          NewVs = lists:umerge(lists:sort(V1s),
                                               lists:sort(V2s)),
  +                       %% Throw an exception (which is equivalent to a no-op)
  +                       %% if there are no differences: if we make multiples
  +                       %% of the exact same thing, stateful() will get confused.
                          false = NewVs == V1s,
                          {read, Pid, LPN, NewVs};
                     ({read, Pid, LPN, Vs}, {result, Pid, Pg}) ->
  
positive.code:                           PidI = {self(), I},
                            event_logger:event(log_make_call(PidI, {read, LPN}),
                                               TS1),
                            Pm = read_result_mangle(P),
                            event_logger:event(log_make_result(PidI, Pm), TS2)
                        end || {{LPN, P}, I} <- PageIs],
                       Ps = [{LPN, read_result_mangle(P)} ||
  
negative.code:           page_size = 0 :: integer(),
            run :: #run{}
           }).
  
  %% Model testing things:
  %% Define true to fake bad behavior that model **must** notice & fail!
  
  -ifndef(TRIP_no_append_duplicates).
  -define(TRIP_no_append_duplicates, false).
  -endif.
  -ifndef(TRIP_bad_read).
  -define(TRIP_bad_read, false).
  -endif.
  -ifndef(TRIP_bad_scan_forward).
  -define(TRIP_bad_scan_forward, false).
  -endif.
  
  initial_state() ->
      #state{}.
  