a third set of {TAIL ~ coefficients} equal to {HEAD ~ −1} extending away from said direction on said second side 
a third set of { TAIL ~ coefficients } equal to { HEAD ~ −1 } extending away from said direction on said second side
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH