anchor.diff:      (make-instance (first (queue factory))
                      :owner (owner factory)
                      :group (group factory)
  -                   :pos (pos factory))))+                   :pos (pos factory))))
  
positive.code:                          :destination (rallying-point factory))
            (current-cost factory)
            (cost (first (queue factory)))))
                           
    (when (>= (progress factory)
              (current-cost factory))
      (setf (current-cost factory)
  
negative.code:              1.2) ;selection indicator must be larger than the unit
            (rot (selected entity))
            (+ 2 (rot (selected entity)))))
  
    (grid-update entity)
    (call-next-method))
  
  