The angle between {TAIL ~ two adjacent light focusing} means 16, 16 is represented by {HEAD ~ A} 
The angle between { TAIL ~ two adjacent light focusing } means 16 , 16 is represented by { HEAD ~ A }
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD