[ while X (slot 0) is not 0
   >> move to Z (slot 2)
   [ loop sets Z to 0
      -
   ]
   < move to Y (slot 1)
   [ if Y is nonzero, set Z to 1
      - decrement Y
      > move to Z
      + set Z to 1
      > move to a slot which will be 0 and terminate the loop
      [ not really necessary unless the next variable is indeterminate
         -
      ]
   ] slot 3 is 0 and pointed to so loop terminates after 1 iteration
   < move to X
   - decrement X
]
>> point to Z
[ if Z is 1 then Y >= X
#If we are here, then Y >= X
   [ set Z to 0 to terminate loop
      -
   ]
]