a-a a-b a-i aaa aab aai aak aao aar aas ab- aba abb abi abk abo abr abs ai- aia aib aii aik aio air ais aka akb aki akk ako akr aks aoa aob aoi aok aoo aor aos ar- ara arb ari ark aro arr ars as- asa asb asi ask aso asr ass baa bab bai bak bao bar bas bba bbb bbi bbk bbo bbr bbs bi- bia bib bii bik bio bir bis bka bkb bkk bko bkr bks boa bob boi bok boo bor bos bra brb bri brk bro brr brs bsa bsb bsi bsk bso bsr bss ia- iaa iab iai iao iar ias iba ibb ibi ibk ibo ibr ibs iia iib iii iio iir iis ika ikb iki ikk iko ikr iks io- ioa iob ioi ioo ior ios ir- ira irb iri irk iro irr irs is- isa isb isi isk iso isr iss ka- kaa kab kai kak kao kar kas kba kbb kbi kbk kbo kbr kbs kia kib kii kik kio kir kis kkb kki kkk kkr kks koa kob koi kok koo kor kos kra kri krk kro krr krs ksa ksb ksi ksk kso ksr kss o-i oaa oab oai oak oao oar oas ob- oba obb obi obk obo obr obs oia oib oii oik oio oir ois oka okb oki okk oko okr oks oo- ooa oob ooi ook ooo oor oos or- ora orb ori ork oro orr ors os- osa osb osi osk oso osr oss ra- raa rab rai rak rao rar ras rba rbb rbi rbk rbo rbr rbs ria rib rii rik rio rir ris rkb rkk rko rks roa rob roi rok roo ror ros rra rrb rri rrk rrr rrs rsa rsb rsi rsk rso rsr rss saa sab sai sak sao sar sas sba sbb sbi sbk sbo sbr sbs sia sib sii sik sio sir sis sk- ska skb ski skk sko skr sks soa sob soi sok soo sor sos sr- sra srb sri srk sro srr srs ss- ssa ssb ssi ssk sso ssr sss