anchor.diff:  
   -type split_step1_failed_reason() :: lease_already_exists.
   
  --type content_check_t() :: fun ((Current::lease_t() | pbr_bottom, 
  +-type content_check_t() :: fun ((Current::lease_t() | prbr_bottom, 
                                    WriteFilter::prbr:write_filter(), 
                                    Next::lease_t()) ->
  -          {Result::boolean(), {Reason::generic_failed_reason(), Current::lease_t() | pbr_bottom, 
  +          {Result::boolean(), {Reason::generic_failed_reason(), Current::lease_t() | prbr_bottom, 
                                  Next::lease_t()} | null}).
   
   -spec delta() -> pos_integer().
  
positive.code:     fun(Current, _WriteFilter, Next) ->
              case Current of
                  % check for prbr_bottom 
                  {prbr_bottom, _WriteFilter, _Next} ->
                      {false, {lease_does_not_exist, pbr_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", 
  
negative.code: % @copyright 2012-2015 Zuse Institute Berlin,
  
  %   Licensed under the Apache License, Version 2.0 (the "License");
  %   you may not use this file except in compliance with the License.
  