-er a-a a-b aaa aab aae aak aao aar aas ab- aba abb abe abk abo abr abs aea aeb aee aek aeo aer aes aka akb ake akk ako akr aks aoa aob aoe aok aoo aor aos ar- ara arb are ark aro arr ars as- asa asb ase ask aso asr ass baa bab bae bak bao bar bas bba bbb bbe bbk bbo bbr bbs be- bea beb bee bek beo ber bes bka bkb bke bkk bko bkr bks boa bob boe bok boo bor bos bra brb bre brk bro brr brs bsa bsb bse bsk bso bsr bss eaa eab eae eak eao ear eas eba ebb ebe ebk ebo ebr ebs eea eeb eee eek eeo eer ees eka ekb eke eko ekr eks eo- eoa eob eoe eok eoo eor eos era erb ere erk ero err ers es- esa esb ese esk eso esr ess ka- kaa kab kae kak kao kar kas kba kbb kbe kbk kbo kbr kbs ke- kea keb kee kek keo ker kes kkb kke kkk kkr kks koa kob koe kok koo kor kos kra krk kro krr krs ksa ksb kse ksk kso ksr kss oaa oab oae oak oao oar oas ob- oba obb obe obk obo obr obs oea oeb oee oeo oer oes oka okb oke okk oko okr oks oo- ooa oob ook ooo oor oos or- ora orb ore ork oro orr ors os- osa osb ose osk oso osr oss ra- raa rab rae rak rao rar ras rba rbb rbe rbk rbo rbr rbs re- rea reb ree rek reo rer res rkb rke rkk rko rks roa rob roe rok roo ror ros rra rrb rrk rrr rrs rsa rsb rse rsk rso rsr rss saa sab sae sak sao sar sas sba sbb sbe sbk sbo sbr sbs se- sea seb see sek seo ser ses sk- ska skb ske skk sko skr sks soa sob soe sok soo sor sos sr- sra srb sre srk sro srr srs ss- ssa ssb sse ssk sso ssr sss