a-a a-b aaa aab aak aan aar aas ab- aba abb abk abn abr abs aka akb akk akn akr aks an- ana anb ank ann anr ans ar- ara arb ark arn arr ars as- asa asb ask asn asr ass baa bab bak ban bar bas bba bbb bbk bbn bbr bbs bka bkb bkk bkn bkr bks bna bnb bnk bnn bnr bns bra brb brk brn brr brs bsa bsb bsk bsn bsr bss ka- kaa kab kak kan kar kas kba kbb kbk kbn kbr kbs kkb kkk kkn kkr kks kn- kna knk knn knr kra krk krn krr krs ksa ksb ksk ksn ksr kss naa nab nak nan nar nas nba nbb nbk nbn nbr nbs nka nkk nkn nkr nks nna nnb nnk nnn nns nra nrb nrk nrn nrr nrs nsa nsb nsk nsn nsr nss ra- raa rab rak ran rar ras rba rbb rbk rbn rbr rbs rkb rkk rks rna rnb rnn rnr rns rra rrb rrk rrn rrr rrs rsa rsb rsk rsn rsr rss saa sab sak san sar sas sba sbb sbk sbn sbr sbs sk- ska skb skk skr sks sna snb snk snn snr sns sr- sra srb srk srn srr srs ss- ssa ssb ssk ssn ssr sss