{HEAD ~ Any method} of {TAIL ~ estimation} may, of course, be adopted provided that the method has practically sufficient accuracy 
of
{ HEAD ~ Any method } of { TAIL ~ estimation } may , of course , be adopted provided that the method has practically sufficient accuracy
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH