a-a aaa aaf aak aao aar aas af- afa aff afk afo afr afs aka akk ako akr aks aoa aof aok aoo aor aos ar- ara arf ark aro arr ars as- asa asf ask aso asr ass faa faf fak fao far fas ffa fff ffk ffo ffr ffs fka fkf fkk foa fof fok foo for fos fra frf frk fro frr frs fsa fsf fsk fso fsr fss ka- kaa kaf kak kao kar kas kfa kff kfo kfs kkk kkr kks koa kof kok koo kor kos kra krf krk kro krr krs ksa ksf ksk kso ksr kss oaa oaf oak oao oar oas of- ofa off ofo ofr ofs oka okk oko okr oks oo- ooa oof ook ooo oor oos or- ora orf ork oro orr ors os- osa osf osk oso osr oss ra- raa raf rak rao rar ras rfa rff rfk rfo rfr rfs rkf rkk rko rks roa rof rok roo ror ros rra rrf rrk rrr rrs rsa rsf rsk rso rsr rss saa saf sak sao sar sas sfa sff sfk sfo sfr sfs sk- ska skf skk sko skr sks soa sof sok soo sor sos sr- sra srf srk sro srr srs ss- ssa ssf ssk sso ssr sss