let rec move_botleft (z : 'a zipper) : 'a zipper =
(* returns z if the targetted node in z has no children *)
- (* else returns move_botleft (zipper which results from moving down and left in z) *)
+ (* else returns move_botleft (zipper which results from moving down from z to the leftmost child) *)
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(* YOU SUPPLY THE DEFINITION *)