An arch 40 is formed in the fold of panels 36 and 38 so as to create {HEAD ~ a downward biasing force} on flaps 36 and 38, which holds {TAIL ~ flaps} 36 and 38 in contact with base 32  
holds
An arch 40 is formed in the fold of panels 36 and 38 so as to create { HEAD ~ a downward biasing force } on flaps 36 and 38 , which holds { TAIL ~ flaps } 36 and 38 in contact with base 32
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH