a-a a-b aaa aab aaf aas aau ab- aba abb abf abs abu af- afa afb aff afs afu as- asa asb asf ass asu au- aua aub auf aus b-u baa bab baf bas bau bba bbb bbf bbs bbu bfa bfb bff bfs bfu bsa bsb bsf bss bsu bua bub buf bus buu faa fab faf fas fau fba fbb fbf fbs fbu ffa fff ffs ffu fsa fsb fsf fss fsu fua fub fuf fus fuu saa sab saf sas sau sba sbb sbf sbs sbu sfa sfb sff sfs sfu ss- ssa ssb ssf sss ssu sua sub suf sus suu ua- uaa uab uaf uas uau uba ubb ubf ubs ubu ufa uff ufs ufu usa usb usf uss usu uua uus uuu