a-a a-b a-c aaa aab aac aak aan aao aar aas ab- aba abb abc abk abn abo abr abs ac- aca acb acc ack acn aco acr acs aka akb akc akk akn ako akr aks an- ana anb anc ank ann ano anr ans aoa aob aoc aok aon aoo aor aos ar- ara arb arc ark arn aro arr ars as- asa asb asc ask asn aso asr ass baa bab bac bak ban bao bar bas bba bbb bbc bbk bbn bbo bbr bbs bca bcb bcc bck bcn bco bcr bcs bka bkb bkc bkk bkn bko bkr bks bna bnb bnc bnk bnn bno bnr bns boa bob boc bok bon boo bor bos bra brb brk brn bro brr brs bsa bsb bsc bsk bsn bso bsr bss c-- caa cab cac cak can cao car cas cba cbb cbc cbk cbn cbo cbr cbs cca ccb ccc cck ccn cco ccr ccs cka ckb ckc cko cks cn- cna cnb cnc cnn cno cnr cns co- coa cob coc cok con coo cor cos cra crb crc crk crn cro crr crs csa csb csc csk csn cso csr css ka- kaa kab kac kak kan kao kar kas kba kbb kbc kbk kbn kbo kbr kbs kca kcb kcc kck kcn kcr kcs kkb kkc kkk kkn kkr kks kn- kna knc knk knn kno knr koa kob koc kok kon koo kor kos kra krc krk krn kro krr krs ksa ksb ksc ksk ksn kso ksr kss naa nab nac nak nan nao nar nas nba nbb nbc nbk nbn nbo nbr nbs nca ncb ncc nck ncn nco ncr ncs nka nkc nkk nkn nko nkr nks nna nnb nnc nnk nnn nno nns no- noa nob noc nok non noo nor nos nra nrb nrc nrk nrn nro nrr nrs nsa nsb nsc nsk nsn nso nsr nss oaa oab oac oak oan oao oar oas ob- oba obb obc obk obn obo obr obs oc- oca ocb occ ock ocn oco ocr ocs oka okb okc okk oko okr oks on- ona onb onc onk onn ono onr ons oo- ooa oob ooc ook oon ooo oor oos or- ora orb orc ork orn oro orr ors os- osa osb osc osk osn oso osr oss ra- raa rab rac rak ran rao rar ras rba rbb rbc rbk rbn rbo rbr rbs rca rcb rcc rcn rco rcr rcs rkb rkc rkk rko rks rna rnb rnc rnn rno rnr rns roa rob roc rok ron roo ror ros rra rrb rrc rrk rrn rrr rrs rsa rsb rsc rsk rsn rso rsr rss saa sab sac sak san sao sar sas sba sbb sbc sbk sbn sbo sbr sbs sca scb scc sck scn sco scr scs sk- ska skb skc skk sko skr sks sna snb snc snk snn sno snr sns soa sob soc sok son soo sor sos sr- sra srb src srk srn sro srr srs ss- ssa ssb ssc ssk ssn sso ssr sss