anchor.diff:  ;;;   * var
   ;;;   * (var)
   ;;;   * (var init-form)
  -;;;   * (var init-from supplied-p-parameter)
  +;;;   * (var init-form supplied-p-parameter)
   ;;;   * ((keyword pattern))
   ;;;   * ((keyword pattern) init-form)
   ;;;   * ((keyword pattern) init-form supplied-p-parameter)
  
positive.code: ;;;   * var
  ;;;   * (var)
  ;;;   * (var init-form)
  ;;;   * (var init-from supplied-p-parameter)
  ;;;   * ((keyword var))
  ;;;   * ((keyword var) init-form)
  ;;;   * ((keyword var) init-form supplied-p-parameter)
  
negative.code: ;;;   * var
  ;;;   * (var)
  ;;;   * (var init-form)
  ;;;   * (var init-form supplied-p-parameter)
  ;;;
  ;;; we boil it down to 2:
  ;;;
  ;;;   * (var init-form)
  ;;;   * (var init-form supplied-p-parameter)
  ;;;
  ;;; by replacing var or (var) by (var nil)
  (defun parse-ordinary-optional (optional)
  