a-a a-b a-c aaa aab aac aak aar aas ab- aba abb abc abk abr abs ac- aca acb acc ack acr acs aka akb akc akk akr aks ar- ara arb arc ark arr ars as- asa asb asc ask asr ass baa bab bac bak bar bas bba bbb bbc bbk bbr bbs bca bcb bcc bck bcr bcs bka bkb bkc bkk bkr bks bra brb brk brr brs bsa bsb bsc bsk bsr bss c-- caa cab cac cak car cas cba cbb cbc cbk cbr cbs cca ccb ccc cck ccr ccs cka ckb ckc cks cra crb crc crk crr crs csa csb csc csk csr css ka- kaa kab kac kak kar kas kba kbb kbc kbk kbr kbs kca kcb kcc kck kcr kcs kkb kkc kkk kkr kks kra krc krk krr krs ksa ksb ksc ksk ksr kss ra- raa rab rac rak rar ras rba rbb rbc rbk rbr rbs rca rcb rcc rcr rcs rkb rkc rkk rks rra rrb rrc rrk rrr rrs rsa rsb rsc rsk rsr rss saa sab sac sak sar sas sba sbb sbc sbk sbr sbs sca scb scc sck scr scs sk- ska skb skc skk skr sks sr- sra srb src srk srr srs ss- ssa ssb ssc ssk ssr sss