a-a a-b a-c a-t aaa aab aac aaf aar aat ab- aba abb abc abf abr abt ac- aca acb acc acf acr act af- afa afb afc aff afr aft ar- ara arb arc arf arr art at- ata atb atc atf atr att baa bab bac baf bar bat bba bbb bbc bbf bbr bbt bca bcb bcc bcf bcr bct bfa bfb bfc bff bfr bft bra brb brf brr brt bta btb btc btf btr btt c-- caa cab cac caf car cat cba cbb cbc cbf cbr cbt cca ccb ccc ccf ccr cct cfa cfb cfc cff cfr cft cra crb crc crf crr crt cta ctb ctc ctf ctr ctt faa fab fac faf far fat fba fbb fbc fbf fbr fbt fca fcb fcc fcf fcr fct ffa ffc fff ffr fft fra frb frc frf frr frt fta ftb ftc ftf ftr ftt ra- raa rab rac raf rar rat rba rbb rbc rbf rbr rbt rca rcb rcc rcf rcr rct rfa rfb rfc rff rfr rft rra rrb rrc rrf rrr rrt rta rtb rtc rtf rtr rtt taa tab tac taf tar tat tba tbb tbc tbf tbr tbt tca tcb tcc tcf tcr tct tfa tfb tfc tff tfr tft tra trb trc trf trr trt tta ttb ttc ttf ttr ttt