a-a a-b a-t a-z aaa aab aar aat aaz ab- aba abb abr abt abz ar- ara arb arr art arz at- ata atb atr att atz az- aza azb azt azz baa bab bar bat baz bba bbb bbr bbt bra brb brr brt brz bta btb btr btt btz bza bzr bzz ra- raa rab rar rat raz rba rbb rbr rbt rra rrb rrr rrt rta rtb rtr rtt rtz rza rzb taa tab tar tat taz tba tbb tbr tbt tbz tra trb trr trt trz tta ttb ttr ttt tza zaa zab zar zat zaz zbb zbr zbt zta ztr zzr zzt zzz