anchor.diff:  %%                              epoch=OldEpoch,version=OldVersion,timeout=OldTimeout} = Old,
   %%                      New, Writer) ->
   %%     fun(prbr_bottom, _WriteFilter, Next) ->
  -%%             {false, {lease_does_not_exist, pbr_bottom, Next}};
  +%%             {false, {lease_does_not_exist, prbr_bottom, Next}};
   %%         (Current, _WriteFilter, Next) when Current =:= New ->
   %%             log:pal("re-write in CC:~n~w~n~w~n~w~n~w~n~w~n", [Current, Next, Old, New, Writer]),
   %%             {true, null};
  
positive.code: 
  -type split_step1_failed_reason() :: lease_already_exists.
  
  -type content_check_t() :: fun ((Current::lease_t() | pbr_bottom, 
                                   WriteFilter::prbr:write_filter(), 
                                   Next::lease_t()) ->
            {Result::boolean(), {Reason::generic_failed_reason(), Current::lease_t() | pbr_bottom, 
                                 Next::lease_t()} | null}).
  
  -spec delta() -> pos_integer().
  
negative.code:     fun(Current, _WriteFilter, Next) ->
              case Current of
                  % check for prbr_bottom 
  %                {prbr_bottom, _WriteFilter, _Next} ->
                  prbr_bottom ->
                      {false, {lease_does_not_exist, prbr_bottom, Next}};
                  % check for re-write
                  New -> % Current =:= New
                      log:pal("re-write in CC:~n~w~n~w~n~w~n~w~n~w~n", 
  