effecting hydrogen bonding between {TAIL ~ mutually complementary portions} of the first and second series fragments to form {HEAD ~ a double stranded structure}; and 
effecting hydrogen bonding between { TAIL ~ mutually complementary portions } of the first and second series fragments to form { HEAD ~ a double stranded structure } ; and
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH