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:                     (Dom,0) -> {Dom,0}
                   end,
            pick=fun(Dom,SampleSize) ->
                         {Dom, random:uniform(min(SampleSize, Diff)) + Min}
                 end
           }.
  
  
negative.code:                            case shrink({_,List1}=Box1) of
                                 {_, List1} ->
                                     {OrigDom1,OrigList1}=OrigBox1,
                                     Index = rand:uniform(length(OrigList1)),
                                     { lists:nth(Index,OrigDom1),
                                       lists:nth(Index,OrigList1) };
  
  