a-a a-b a-c a-t aaa aab aac aar aas aat ab- aba abb abc abr abs abt ac- aca acb acc acr acs act ar- ara arb arc arr ars art as- asa asb asc asr ass ast at- ata atb atc atr ats att baa bab bac bar bas bat bba bbb bbc bbr bbs bbt bca bcb bcc bcr bcs bct bra brb brr brs brt bsa bsb bsc bsr bss bst bta btb btc btr bts btt c-- caa cab cac car cas cat cba cbb cbc cbr cbs cbt cca ccb ccc ccr ccs cct cra crb crc crr crs crt csa csb csc csr css cst cta ctb ctc ctr cts ctt ra- raa rab rac rar ras rat rba rbb rbc rbr rbs rbt rca rcb rcc rcr rcs rct rra rrb rrc rrr rrs rrt rsa rsb rsc rsr rss rst rta rtb rtc rtr rts rtt saa sab sac sar sas sat sba sbb sbc sbr sbs sbt sca scb scc scr scs sct sr- sra srb src srr srs srt ss- ssa ssb ssc ssr sss sst sta stb stc str sts stt taa tab tac tar tas tat tba tbb tbc tbr tbs tbt tca tcb tcc tcr tcs tct tra trb trc trr trs trt tsa tsb tsc tsr tss tst tta ttb ttc ttr tts ttt