anchor.diff:  
   (defmethod expiredp ((behavior behavior) current-time)
     (>= current-time (expiration behavior)))
  -
  -(defgeneric evaluate-situation (mover))
   
   (defmethod evaluate-situation ((sheep sheep))
     (let* ((others (remove-if (lambda (x) (eq x sheep)) (herd sheep)))
  
positive.code:    (max-speed
      :initarg :max-speed
      :accessor max-speed
      :initform (error "must supply a max speed"))
  ))
  
  (defclass sheep (mover)
    ((name
  
negative.code: (in-package :village)
  
  (defparameter *parent-lines-visible-p* nil)
  (defparameter *sheep-labels-visible-p* nil)
  (defparameter *heading-indicators-visible-p* nil)
  (defparameter *color-sheep-by-status-p* t)
  
  (defgeneric add-actor (environment actor))
  (defgeneric draw (cr object))
  