a-a a-b aaa aab aae aak aao aas ab- aba abb abe abk abo abs aea aeb aee aek aeo aes aka akb ake akk ako aks aoa aob aoe aok aoo aos as- asa asb ase ask aso ass baa bab bae bak bao bas bba bbb bbe bbk bbo bbs be- bea beb bee bek beo bes bka bkb bke bkk bko bks boa bob boe bok boo bos bsa bsb bse bsk bso bss eaa eab eae eak eao eas eba ebb ebe ebk ebo ebs eea eeb eee eek eeo ees eka ekb eke eko eks eo- eoa eob eoe eok eoo eos es- esa esb ese esk eso ess ka- kaa kab kae kak kao kas kba kbb kbe kbk kbo kbs ke- kea keb kee kek keo kes kkb kke kkk kks koa kob koe kok koo kos ksa ksb kse ksk kso kss oaa oab oae oak oao oas ob- oba obb obe obk obo obs oea oeb oee oeo oes oka okb oke okk oko oks oo- ooa oob ook ooo oos os- osa osb ose osk oso oss saa sab sae sak sao sas sba sbb sbe sbk sbo sbs se- sea seb see sek seo ses sk- ska skb ske skk sko sks soa sob soe sok soo sos ss- ssa ssb sse ssk sso sss