anchor.diff:    (struct :tag "symbol" :contents (random-string)))
   
   (defun random-type () :hidden
  -  (let* [(types '("symbol" "boolean" "number" "string" "key"
  -                  "list"))]
  +  (let* [(types '("symbol" "boolean" "number" "string" "key" "list"))]
       (nth types (random 1 (# types)))))
   
   (defun -random-type () :hidden
  
positive.code:     ["number" (random-number)]
      ["symbol" (random-symbol)]
      ["key" (random-string)]
      ["list" (random-list)]))
  
  (defun random-list () :hidden
    (let* [(length (random 1 2))]
  
negative.code:                           ,ctr " iteration(s).\n Falsifying set of values:\n"
                            ,@(map make-printing bindings))))
                      (inc! ,ctr)))
                  )))]
      `(let* ,(map generate-binding bindings)
         ,@(map generate-body props))))
  