anchor.diff:           bucket_size    = 24                :: pos_integer(),   %max items in a leaf
            signature_size = 4                 :: pos_integer(),   %node signature size in byte
            leaf_hf        = fun(V) -> ?CRYPTO_SHA(V) end  :: hash_fun(),      %hash function for leaf signature creation
  -         inner_hf       = get_XOR_fun()     :: inner_hash_fun(),%hash function for inner node signature creation -
  +         inner_hf       = fun inner_hash_XOR/1 :: inner_hash_fun(),%hash function for inner node signature creation -
            keep_bucket    = false             :: boolean()        %false=bucket will be empty after bulk_build; true=bucket will be filled
            }).
   -type mt_config() :: #mt_config{}.
  
positive.code: 
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
  -spec get_XOR_fun() -> inner_hash_fun().
  get_XOR_fun() ->
      fun([H|T]) -> lists:foldl(fun(X, Acc) -> X bxor Acc end, H, T) end.
  
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
  
negative.code: 
  % allow future versions to create more hash funs by having an integer parameter
  -spec tester_create_inner_hash_fun(I::1) -> inner_hash_fun().
  tester_create_inner_hash_fun(1) -> fun inner_hash_XOR/1.
  