The subtrahend is stored in the A register and {TAIL ~ the minuend} in {HEAD ~ the B} register 
The subtrahend is stored in the A register and { TAIL ~ the minuend } in { HEAD ~ the B } register
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH