A server receives an interaction history comprising a set of one to {HEAD ~ one interactions} between a first user and {TAIL ~ other users} 
between
A server receives an interaction history comprising a set of one to { HEAD ~ one interactions } between a first user and { TAIL ~ other users }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL