{HEAD ~ mounting fixtures} configured to mount said {TAIL ~ device} on a head of said first user, 
configured to mount
{ HEAD ~ mounting fixtures } configured to mount said { TAIL ~ device } on a head of said first user ,
HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH