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