beginning a control cycle when {HEAD ~ Ri} is between {TAIL ~ Ro+r} and Ro r 
is between
beginning a control cycle when { HEAD ~ Ri } is between { TAIL ~ Ro+r } and Ro r
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH