a-a a-b aaa aab aak aar aas ab- aba abb abk abr abs aka akb akk akr aks ar- ara arb ark arr ars as- asa asb ask asr ass baa bab bak bar bas bba bbb bbk bbr bbs bka bkb bkk bkr bks bra brb brk brr brs bsa bsb bsk bsr bss ka- kaa kab kak kar kas kba kbb kbk kbr kbs kkb kkk kkr kks kra krk krr krs ksa ksb ksk ksr kss ra- raa rab rak rar ras rba rbb rbk rbr rbs rkb rkk rks rra rrb rrk rrr rrs rsa rsb rsk rsr rss saa sab sak sar sas sba sbb sbk sbr sbs sk- ska skb skk skr sks sr- sra srb srk srr srs ss- ssa ssb ssk ssr sss