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