anchor.diff:  
   (def form-class auxiliary-function-argument-form (function-argument-form-with-default-value)
     ())
  -
  -(defun walk-auxiliary-argument (form parent env)
  -  (destructuring-bind (name &optional (default-value nil default-value-supplied?))
  -      (ensure-list form)
  -    (with-form-object (arg 'auxiliary-function-argument-form parent :name name)
  -      (when default-value-supplied?
  -        (setf (default-value-of arg) (walk-form default-value :parent arg :environment env))))))
   
   (def unwalker auxiliary-function-argument-form (name supplied-p-parameter)
     (bind ((default-value (awhen (default-value-of -form-)
  
positive.code:     ast-node))
  
  (def (function e) walk-ordinary-lambda-list (lambda-list parent env &key allow-specializers)
    (flet ((augment! (walked)
             (augment-walk-environment! env :variable (name-of walked) walked)
             walked))
      (bind (((:values requireds optionals rest keywords allow-other-keys? auxiliaries) (parse-ordinary-lambda-list lambda-list :normalize nil))
             (result (nconc
                      (loop
                        :for required :in requireds
                        :collect (augment! (if allow-specializers
                                               (walk-specialized-argument required parent env)
                                               (make-form-object 'required-function-argument-form parent :name required))))
                      (loop
                        :for optional :in optionals
                        :collect (augment! (walk-optional-argument optional parent env)))
                      (when rest
                        (list (augment! (make-form-object 'rest-function-argument-form parent :name rest))))
                      (loop
                        :for keyword :in keywords
                        :collect (augment! (walk-keyword-argument keyword parent env)))
                      (when allow-other-keys?
                        (list (make-form-object 'allow-other-keys-function-argument-form parent)))
                      (loop
                        :for auxiliary :in auxiliaries
                        :collect (augment! (walk-auxiliary-argument auxiliary parent env))))))
        (values result env))))
  
  (def form-class function-argument-form (name-definition-form)
    ())
  
negative.code: 
  (def form-class optional-function-argument-form (function-argument-form-with-supplied-p-parameter)
    ())
  
  (def unwalker optional-function-argument-form (name supplied-p-parameter-name)
    (bind ((default-value (awhen (default-value-of -form-)
  