a-a a-b a-t aaa aab aaf aao aat aax ab- aba abb abf abo abt abx af- afa afb aff afo aft afx aoa aob aof aoo aot aox at- ata atb atf ato att atx ax- axa axo axt axx baa bab baf bao bat bax bba bbb bbf bbo bbt bbx bfa bfb bff bfo bft bfx boa bob bof boo bot box bta btb btf bto btt btx bxb bxo bxx faa fab faf fao fat fax fba fbb fbf fbo fbt fbx ffa fff ffo fft ffx foa fob fof foo fot fox fta ftb ftf fto ftt ftx fxt fxx oaa oab oaf oao oat oax ob- oba obb obf obo obt obx of- ofa ofb off ofo oft ofx oo- ooa oob oof ooo oot oox ot- ota otb otf oto ott ox- oxa oxb oxf oxo oxt oxx t-x taa tab taf tao tat tax tba tbb tbf tbo tbt tfa tfb tff tfo tft tfx to- toa tob tof too tot tox tta ttb ttf tto ttt ttx txf txt xaa xaf xat xbx xfa xft xfx xoa xof xoo xot xox xtf xtx xxo xxx