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