In {TAIL ~ alternate embodiments}, stacking arrangements include: {HEAD ~ gamma structures} alone; or delta structures alone 
In { TAIL ~ alternate embodiments } , stacking arrangements include : { HEAD ~ gamma structures } alone ; or delta structures alone
OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH