a-a a-b aaa aab aak aan aao aar aas ab- aba abb abk abn abo abr abs aka akb akk akn ako akr aks an- ana anb ank ann ano anr ans aoa aob aok aon aoo aor aos ar- ara arb ark arn aro arr ars as- asa asb ask asn aso asr ass baa bab bak ban bao bar bas bba bbb bbk bbn bbo bbr bbs bka bkb bkk bkn bko bkr bks bna bnb bnk bnn bno bnr bns boa bob bok bon boo bor bos bra brb brk brn bro brr brs bsa bsb bsk bsn bso bsr bss ka- kaa kab kak kan kao kar kas kba kbb kbk kbn kbo kbr kbs kkb kkk kkn kkr kks kn- kna knk knn kno knr koa kob kok kon koo kor kos kra krk krn kro krr krs ksa ksb ksk ksn kso ksr kss naa nab nak nan nao nar nas nba nbb nbk nbn nbo nbr nbs nka nkk nkn nko nkr nks nna nnb nnk nnn nno nns no- noa nob nok non noo nor nos nra nrb nrk nrn nro nrr nrs nsa nsb nsk nsn nso nsr nss oaa oab oak oan oao oar oas ob- oba obb obk obn obo obr obs oka okb okk oko okr oks on- ona onb onk onn ono onr ons oo- ooa oob ook oon ooo oor oos or- ora orb ork orn oro orr ors os- osa osb osk osn oso osr oss ra- raa rab rak ran rao rar ras rba rbb rbk rbn rbo rbr rbs rkb rkk rko rks rna rnb rnn rno rnr rns roa rob rok ron roo ror ros rra rrb rrk rrn rrr rrs rsa rsb rsk rsn rso rsr rss saa sab sak san sao sar sas sba sbb sbk sbn sbo sbr sbs sk- ska skb skk sko skr sks sna snb snk snn sno snr sns soa sob sok son soo sor sos sr- sra srb srk srn sro srr srs ss- ssa ssb ssk ssn sso ssr sss