a-a a-b a-t aaa aab aan aar aat ab- aba abb abn abr abt an- ana anb ann anr ant ar- ara arb arn arr art at- ata atb atn atr att baa bab ban bar bat bba bbb bbn bbr bbt bna bnb bnn bnr bnt bra brb brn brr brt bta btb btn btr btt naa nab nan nar nat nba nbb nbn nbr nbt nna nnb nnn nnt nra nrb nrn nrr nrt nta ntb ntn ntr ntt ra- raa rab ran rar rat rba rbb rbn rbr rbt rna rnb rnn rnr rnt rra rrb rrn rrr rrt rta rtb rtn rtr rtt taa tab tan tar tat tba tbb tbn tbr tbt tna tnb tnn tnr tnt tra trb trn trr trt tta ttb ttn ttr ttt