One of the strips is then turned end to end without rotation, so that {HEAD ~ both faces} on the upper surface are either inner faces or {TAIL ~ outer faces} 
are
One of the strips is then turned end to end without rotation , so that { HEAD ~ both faces } on the upper surface are either inner faces or { TAIL ~ outer faces }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL