Homology or {HEAD ~ identity} can be determined by comparing {TAIL ~ a position} in each sequence which may be aligned for purposes of comparison 
Homology or { HEAD ~ identity } can be determined by comparing { TAIL ~ a position } in each sequence which may be aligned for purposes of comparison
OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH