When {HEAD ~ a first mobile user} wants a second mobile user to follow him, {TAIL ~ the first mobile user} can put his device in “follow me” mode 
When { HEAD ~ a first mobile user } wants a second mobile user to follow him , { TAIL ~ the first mobile user } can put his device in “ follow me ” mode
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH