a-a a-b a-t aaa aab aao aat aay ab- aba abb abo abt aby aoa aob aoo aot at- ata atb ato att ay- aya ayo ayt baa bab bao bat bay bba bbb bbo bbt bby boa bob boo bot boy bta btb bto btt bty by- bya byo byt oaa oab oao oat ob- oba obb obo obt oby oo- ooa oob ooo oot ot- ota otb oto ott oya oyo taa tab tao tat tay tba tbb tbo tbt to- toa tob too tot toy tta ttb tto ttt tty tya tyo tyt yaa yab yao yat yay yby yob yoo yot yoy yta yto ytt yyb yyt yyy