a-a a-b aaa aab aae aaf aak aao aas ab- aba abb abe abf abk abo abs aea aeb aee aef aek aeo aes af- afa afb afe aff afk afo afs aka akb ake akk ako aks aoa aob aoe aof aok aoo aos as- asa asb ase asf ask aso ass baa bab bae baf bak bao bas bba bbb bbe bbf bbk bbo bbs be- bea beb bee bef bek beo bes bfa bfb bfe bff bfo bfs bka bkb bke bkf bkk bko bks boa bob boe bof bok boo bos bsa bsb bse bsf bsk bso bss eaa eab eae eaf eak eao eas eba ebb ebe ebf ebk ebo ebs eea eeb eee eef eek eeo ees ef- efa efb efe eff efo efs eka ekb eke ekf eko eks eo- eoa eob eoe eof eok eoo eos es- esa esb ese esf esk eso ess faa fab fae faf fak fao fas fba fbb fbe fbf fbk fbo fbs fea feb fee fef fek feo fes ffa ffe fff ffk ffo ffs fka fkb fkf fkk foa fob foe fof fok foo fos fsa fsb fse fsf fsk fso fss ka- kaa kab kae kaf kak kao kas kba kbb kbe kbf kbk kbo kbs ke- kea keb kee kef kek keo kes kfa kff kfo kfs kkb kke kkk kks koa kob koe kof kok koo kos ksa ksb kse ksf ksk kso kss oaa oab oae oaf oak oao oas ob- oba obb obe obf obk obo obs oea oeb oee oef oeo oes of- ofa ofb ofe off ofo ofs oka okb oke okk oko oks oo- ooa oob oof ook ooo oos os- osa osb ose osf osk oso oss saa sab sae saf sak sao sas sba sbb sbe sbf sbk sbo sbs se- sea seb see sef sek seo ses sfa sfb sfe sff sfk sfo sfs sk- ska skb ske skf skk sko sks soa sob soe sof sok soo sos ss- ssa ssb sse ssf ssk sso sss