anchor.diff:  
   -spec random_unicode_char() -> uchar().
   random_unicode_char() ->
  -    case (random:uniform(16#10FFFF + 1) - 1) of
  +    case (rand:uniform(16#10FFFF + 1) - 1) of
           C when C >= 16#D800 andalso C =< 16#DFFF ->
               %% surrogates
               random_unicode_char();
  
positive.code:             end;
          3 -> %% Remove a random sublist.
              Zipped = lists:zip(ListDom, List),
              TrueTreshold  = random:uniform(),
              FalseTreshold = random:uniform(),
              %% This may happen to be the original list again.
              Pruned = markov_prune_list(Zipped, TrueTreshold, FalseTreshold,
                                         false),
  
negative.code:     %%
      %% replace element at RemIdx with simplified one
      %%
      RemIdx = rand:uniform(Len),
      Elm = lists:nth(RemIdx, List),
      ElmDom = lists:nth(RemIdx, ListDom),
  
  