a-a a-b a-c aaa aab aac aan aao aar aas ab- aba abb abc abn abo abr abs ac- aca acb acc acn aco acr acs an- ana anb anc ann ano anr ans aoa aob aoc aon aoo aor aos ar- ara arb arc arn aro arr ars as- asa asb asc asn aso asr ass baa bab bac ban bao bar bas bba bbb bbc bbn bbo bbr bbs bca bcb bcc bcn bco bcr bcs bna bnb bnc bnn bno bnr bns boa bob boc bon boo bor bos bra brb brn bro brr brs bsa bsb bsc bsn bso bsr bss c-- caa cab cac can cao car cas cba cbb cbc cbn cbo cbr cbs cca ccb ccc ccn cco ccr ccs cn- cna cnb cnc cnn cno cnr cns co- coa cob coc con coo cor cos cra crb crc crn cro crr crs csa csb csc csn cso csr css naa nab nac nan nao nar nas nba nbb nbc nbn nbo nbr nbs nca ncb ncc ncn nco ncr ncs nna nnb nnc nnn nno nns no- noa nob noc non noo nor nos nra nrb nrc nrn nro nrr nrs nsa nsb nsc nsn nso nsr nss oaa oab oac oan oao oar oas ob- oba obb obc obn obo obr obs oc- oca ocb occ ocn oco ocr ocs on- ona onb onc onn ono onr ons oo- ooa oob ooc oon ooo oor oos or- ora orb orc orn oro orr ors os- osa osb osc osn oso osr oss ra- raa rab rac ran rao rar ras rba rbb rbc rbn rbo rbr rbs rca rcb rcc rcn rco rcr rcs rna rnb rnc rnn rno rnr rns roa rob roc ron roo ror ros rra rrb rrc rrn rrr rrs rsa rsb rsc rsn rso rsr rss saa sab sac san sao sar sas sba sbb sbc sbn sbo sbr sbs sca scb scc scn sco scr scs sna snb snc snn sno snr sns soa sob soc son soo sor sos sr- sra srb src srn sro srr srs ss- ssa ssb ssc ssn sso ssr sss