a-a a-b a-t aaa aab aad aar aat ab- aba abb abd abr abt ad- ada adb add adr adt ar- ara arb ard arr art at- ata atb atd atr att baa bab bad bar bat bba bbb bbd bbr bbt bda bdb bdd bdr bdt bra brb brd brr brt bta btb btd btr btt daa dab dad dar dat dba dbb dbd dbr dbt dda ddb ddd ddr ddt dra drb drd drr drt dta dtb dtd dtr dtt ra- raa rab rad rar rat rba rbb rbd rbr rbt rda rdb rdd rdr rdt rra rrb rrd rrr rrt rta rtb rtd rtr rtt taa tab tad tar tat tba tbb tbd tbr tbt tda tdb tdd tdr tdt tra trb trd trr trt tta ttb ttd ttr ttt