eee eef eeo eet eex ef- efe eff efo eft efx eo- eoe eof eoo eot ete etf eto ett etx ex- exe exo ext exx fee fef feo fet fex ffe fff ffo fft ffx foe fof foo fot fox fte ftf fto ftt ftx fxe fxt fxx oee oef oeo oet oex of- ofe off ofo oft ofx oo- oof ooo oot oox ot- ote otf oto ott ox- oxf oxo oxt oxx t-x te- tee tef teo tet tex tfe tff tfo tft tfx to- toe tof too tot tox tte ttf tto ttt ttx txe txf txt xee xet xex xfe xft xfx xof xoo xot xox xtf xtx xxo xxx