anchor.diff:  
   (def form-class optional-function-argument-form (function-argument-form-with-supplied-p-parameter)
     ())
  -
  -(defun walk-optional-argument (form parent env)
  -  ;; TODO report bind bug: (bind (((name &optional (default-value nil default-value-supplied?) supplied-p-parameter) (ensure-list form))) )
  -  (destructuring-bind (name &optional (default-value nil default-value-supplied?) supplied-p-parameter-name)
  -      (ensure-list form)
  -    (with-form-object (arg 'optional-function-argument-form parent
  -                           :name name
  -                           :supplied-p-parameter-name supplied-p-parameter-name)
  -      (when default-value-supplied?
  -        (setf (default-value-of arg) (walk-form default-value :parent arg :environment env))))))
   
   (def unwalker optional-function-argument-form (name supplied-p-parameter-name)
     (bind ((default-value (awhen (default-value-of -form-)
  
positive.code: 
  (def form-class specialized-function-argument-form (required-function-argument-form)
    ((specializer)))
  
  (def function walk-specialized-argument (form parent env)
    (declare (ignore env))
    (make-form-object 'specialized-function-argument-form parent
                      :name (if (listp form)
                                (first form)
                                form)
                      :specializer (if (listp form)
                                       (second form)
                                       t)))
  
  (def unwalker specialized-function-argument-form (name specializer)
    (if (eq specializer t)
  
negative.code: 
  (def form-class auxiliary-function-argument-form (function-argument-form-with-default-value)
    ())
  
  (def unwalker auxiliary-function-argument-form (name supplied-p-parameter)
    (bind ((default-value (awhen (default-value-of -form-)
  