a-a a-b a-t aaa aab aar aat aay ab- aba abb abr abt aby ar- ara arb arr art ary at- ata atb atr att ay- aya ayr ayt baa bab bar bat bay bba bbb bbr bbt bby bra brb brr brt bry bta btb btr btt bty by- bya byr byt ra- raa rab rar rat ray rba rbb rbr rbt rra rrb rrr rrt rta rtb rtr rtt rty ry- rya ryr ryy taa tab tar tat tay tba tbb tbr tbt tra trb trr trt try tta ttb ttr ttt tty tya tyr tyt yaa yab yar yat yay ybr yby yra yrt yta ytr ytt yyb yyt yyy