{HEAD ~ The content} of {TAIL ~ Mn}, if any, is preferably from 1 to 9 mol % 
of
{ HEAD ~ The content } of { TAIL ~ Mn } , if any , is preferably from 1 to 9 mol %
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH