(let
((,new-patch (patch-at (turtle-xcor ,turtle) (turtle-ycor ,turtle))))
(when (not (eql ,patch ,new-patch))
(setf (patch-turtles ,patch) (remove ,turtle (patch-turtles ,patch)))
(let
((,new-patch (patch-at (turtle-xcor ,turtle) (turtle-ycor ,turtle))))
(when (not (eql ,patch ,new-patch))
(setf (patch-turtles ,patch) (remove ,turtle (patch-turtles ,patch)))