anchor.diff:  (defparameter *acceleration* nil)
   (defparameter *mouse* nil)
   (defparameter *center* nil)
  +(defparameter *movers* nil)
   
   (defparameter *x* 0)
   (defparameter *y* 0)
  
positive.code: (defclass pvector ()
    ((x :initarg :x :initform 0 :accessor x)
     (y :initarg :y :initform 0 :accessor y)))
  
  (defun equal-vectors (vec-1 vec-2)
    (setf (x vec-1) (x vec-2))
  
negative.code:   (format t "> motion-101~%")
    (format t "> motion-101-acceleration~%")
    (format t "> motion-101-random-acceleration~%")
    (format t "> motion-101-acceleration-towards-mouse~%")
    (format t "> motion-101-array-movers-towards-mouse~%"))
  