In {HEAD ~ preferred embodiments}, each of {TAIL ~ x} and y, independently, is an integer between about 2 and 6 
In { HEAD ~ preferred embodiments } , each of { TAIL ~ x } and y , independently , is an integer between about 2 and 6
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH