a-a a-b a-c a-t aaa aab aac aar aat ab- aba abb abc abr abt ac- aca acb acc acr act ar- ara arb arc arr art at- ata atb atc atr att baa bab bac bar bat bba bbb bbc bbr bbt bca bcb bcc bcr bct bra brb brr brt bta btb btc btr btt c-- caa cab cac car cat cba cbb cbc cbr cbt cca ccb ccc ccr cct cra crb crc crr crt cta ctb ctc ctr ctt ra- raa rab rac rar rat rba rbb rbc rbr rbt rca rcb rcc rcr rct rra rrb rrc rrr rrt rta rtb rtc rtr rtt taa tab tac tar tat tba tbb tbc tbr tbt tca tcb tcc tcr tct tra trb trc trr trt tta ttb ttc ttr ttt