a-a a-b a-c aaa aab aac aan aar aas ab- aba abb abc abn abr abs ac- aca acb acc acn acr acs an- ana anb anc ann anr ans ar- ara arb arc arn arr ars as- asa asb asc asn asr ass baa bab bac ban bar bas bba bbb bbc bbn bbr bbs bca bcb bcc bcn bcr bcs bna bnb bnc bnn bnr bns bra brb brn brr brs bsa bsb bsc bsn bsr bss c-- caa cab cac can car cas cba cbb cbc cbn cbr cbs cca ccb ccc ccn ccr ccs cn- cna cnb cnc cnn cnr cns cra crb crc crn crr crs csa csb csc csn csr css naa nab nac nan nar nas nba nbb nbc nbn nbr nbs nca ncb ncc ncn ncr ncs nna nnb nnc nnn nns nra nrb nrc nrn nrr nrs nsa nsb nsc nsn nsr nss ra- raa rab rac ran rar ras rba rbb rbc rbn rbr rbs rca rcb rcc rcn rcr rcs rna rnb rnc rnn rnr rns rra rrb rrc rrn rrr rrs rsa rsb rsc rsn rsr rss saa sab sac san sar sas sba sbb sbc sbn sbr sbs sca scb scc scn scr scs sna snb snc snn snr sns sr- sra srb src srn srr srs ss- ssa ssb ssc ssn ssr sss