anchor.diff:      let
         len = length list;
         foldl' = n:
  -        if n == -1
  -        then nul
  -        else op (foldl' (n - 1)) (elemAt list n);
  -    in foldl' (length list - 1);
  +        if n == -1 then
  +          nul
  +        else
  +          op (foldl' (n - 1)) (elemAt list n);
  +    in
  +    foldl' (length list - 1);
   
   
     # Strict version of foldl.
  
positive.code: 
  rec {
  
    inherit (builtins) head tail length isList elemAt concatLists filter elem genList;
  
  
    # Create a list consisting of a single element.  `singleton x' is
    # sometimes more convenient with respect to indentation than `[x]'
    # when x spans multiple lines.
    singleton = x: [x];
  
  
    # "Fold" a binary function `op' between successive elements of
  
negative.code:           if n != len then
              [ (f (elemAt fst n) (elemAt snd n)) ]
              ++ zipListsWith' (n + 1)
            else [ ];
        in
        zipListsWith' 0;
  
    zipLists = zipListsWith (fst: snd: { inherit fst snd; });
  
  