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