a-a a-b a-t aaa aab aao aat aax ab- aba abb abo abt abx aoa aob aoo aot aox at- ata atb ato att atx ax- axa axo axt axx baa bab bao bat bax bba bbb bbo bbt bbx boa bob boo bot box bta btb bto btt btx bxb bxo bxx oaa oab oao oat oax ob- oba obb obo obt obx oo- ooa oob ooo oot oox ot- ota otb oto ott ox- oxa oxb oxo oxt oxx t-x taa tab tao tat tax tba tbb tbo tbt to- toa tob too tot tox tta ttb tto ttt ttx txt xaa xat xbx xoa xoo xot xox xtx xxo xxx