a-a a-b a-c a-t aaa aab aac aao aas aat ab- aba abb abc abo abs abt ac- aca acb acc aco acs act aoa aob aoc aoo aos aot as- asa asb asc aso ass ast at- ata atb atc ato ats att baa bab bac bao bas bat bba bbb bbc bbo bbs bbt bca bcb bcc bco bcs bct boa bob boc boo bos bot bsa bsb bsc bso bss bst bta btb btc bto bts btt c-- caa cab cac cao cas cat cba cbb cbc cbo cbs cbt cca ccb ccc cco ccs cct co- coa cob coc coo cos cot csa csb csc cso css cst cta ctb ctc cto cts ctt oaa oab oac oao oas oat ob- oba obb obc obo obs obt oc- oca ocb occ oco ocs oct oo- ooa oob ooc ooo oos oot os- osa osb osc oso oss ost ot- ota otb otc oto ots ott saa sab sac sao sas sat sba sbb sbc sbo sbs sbt sca scb scc sco scs sct soa sob soc soo sos sot ss- ssa ssb ssc sso sss sst sta stb stc sto sts stt taa tab tac tao tas tat tba tbb tbc tbo tbs tbt tca tcb tcc tco tcs tct to- toa tob toc too tos tot tsa tsb tsc tso tss tst tta ttb ttc tto tts ttt