{TAIL ~ These operations} of {HEAD ~ vertical and horizontal edges} can be expanded to have coefficients of a, −a, 0, or aj as before 
{ TAIL ~ These operations } of { HEAD ~ vertical and horizontal edges } can be expanded to have coefficients of a , −a , 0 , or aj as before
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH