The elements of are the set of exponents dk+1, {HEAD ~ i.e. exponents} of {TAIL ~ σ} 
of
The elements of are the set of exponents dk+1 , { HEAD ~ i.e. exponents } of { TAIL ~ σ }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL