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