In {TAIL ~ operation}, {HEAD ~ customers} enter into waiting line 16 thus activating the entrance detector 18 
In
In { TAIL ~ operation } , { HEAD ~ customers } enter into waiting line 16 thus activating the entrance detector 18
REL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH