In {TAIL ~ another implementation}, the second mobile device could also optionally present {HEAD ~ a distance} to the first mobile device 
In { TAIL ~ another implementation } , the second mobile device could also optionally present { HEAD ~ a distance } to the first mobile device
OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH