anchor.diff:    */
     singleton = x: [x];
   
  -  /* “right fold” a binary function `op' between successive elements of
  -     `list' with `nul' as the starting value, i.e.,
  -     `foldr op nul [x_1 x_2 ... x_n] == op x_1 (op x_2 ... (op x_n nul))'.
  -     Type:
  -       foldr :: (a -> b -> b) -> b -> [a] -> b
  +  /* “right fold” a binary function `op` between successive elements of
  +     `list` with `nul' as the starting value, i.e.,
  +     `foldr op nul [x_1 x_2 ... x_n] == op x_1 (op x_2 ... (op x_n nul))`.
  +
  +     Type: foldr :: (a -> b -> b) -> b -> [a] -> b
   
        Example:
          concat = foldr (a: b: a + b) "z"
  
positive.code:     assert lib.assertMsg (list != []) "lists.last: list must not be empty!";
      elemAt list (length list - 1);
  
    /* Return all elements but the last
  
       Example:
         init [ 1 2 3 ]
  
negative.code:                 rest    = [ "/home" "other" ];  # everything else
  
     */
    listDfs = stopOnCycles: before: list:
      let
        dfs' = us: visited: rest:
  