A pair of {HEAD ~ modules} may be combined to have {TAIL ~ a common plane reflector}, and the pairs may be further combined if desired 
A pair of { HEAD ~ modules } may be combined to have { TAIL ~ a common plane reflector } , and the pairs may be further combined if desired
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH