a-a a-b a-c aaa aab aac aak aao aar aas ab- aba abb abc abk abo abr abs ac- aca acb acc ack aco acr acs aka akb akc akk ako akr aks aoa aob aoc aok aoo aor aos ar- ara arb arc ark aro arr ars as- asa asb asc ask aso asr ass baa bab bac bak bao bar bas bba bbb bbc bbk bbo bbr bbs bca bcb bcc bck bco bcr bcs bka bkb bkc bkk bko bkr bks boa bob boc bok boo bor bos bra brb brk bro brr brs bsa bsb bsc bsk bso bsr bss c-- caa cab cac cak cao car cas cba cbb cbc cbk cbo cbr cbs cca ccb ccc cck cco ccr ccs cka ckb ckc cko cks co- coa cob coc cok coo cor cos cra crb crc crk cro crr crs csa csb csc csk cso csr css ka- kaa kab kac kak kao kar kas kba kbb kbc kbk kbo kbr kbs kca kcb kcc kck kcr kcs kkb kkc kkk kkr kks koa kob koc kok koo kor kos kra krc krk kro krr krs ksa ksb ksc ksk kso ksr kss oaa oab oac oak oao oar oas ob- oba obb obc obk obo obr obs oc- oca ocb occ ock oco ocr ocs oka okb okc okk oko okr oks oo- ooa oob ooc ook ooo oor oos or- ora orb orc ork oro orr ors os- osa osb osc osk oso osr oss ra- raa rab rac rak rao rar ras rba rbb rbc rbk rbo rbr rbs rca rcb rcc rco rcr rcs rkb rkc rkk rko rks roa rob roc rok roo ror ros rra rrb rrc rrk rrr rrs rsa rsb rsc rsk rso rsr rss saa sab sac sak sao sar sas sba sbb sbc sbk sbo sbr sbs sca scb scc sck sco scr scs sk- ska skb skc skk sko skr sks soa sob soc sok soo sor sos sr- sra srb src srk sro srr srs ss- ssa ssb ssc ssk sso ssr sss