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