User interface 520 may include mechanisms for inputting information to {HEAD ~ user device} 210 and for outputting information from {TAIL ~ user device} 210 
User interface 520 may include mechanisms for inputting information to { HEAD ~ user device } 210 and for outputting information from { TAIL ~ user device } 210
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH