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