{HEAD ~ The velocity} of the progression is determined by {TAIL ~ the given distance} of the fixtures at a given frequency 
is determined by
{ HEAD ~ The velocity } of the progression is determined by { TAIL ~ the given distance } of the fixtures at a given frequency
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH