-bind (unit ann) (thinks (bind (unit bill) left)) 1;;
-bind (unit ann) (thinks (bind (unit cam) left)) 1;;
+(mid bill >>= left) 1;; (* true *)
+(mid cam >>= left) 1;; (* true *)
+(mid ann >>= thinks (mid bill >>= left)) 1;; (* true *)
+(mid ann >>= thinks (mid cam >>= left)) 1;; (* false *)