a-a a-b a-t aaa aab aae aaf aao aat ab- aba abb abe abf abo abt aea aeb aee aef aeo aet af- afa afb afe aff afo aft aoa aob aoe aof aoo aot at- ata atb ate atf ato att baa bab bae baf bao bat bba bbb bbe bbf bbo bbt be- bea beb bee bef beo bet bfa bfb bfe bff bfo bft boa bob boe bof boo bot bta btb bte btf bto btt eaa eab eae eaf eao eat eba ebb ebe ebf ebo ebt eea eeb eee eef eeo eet ef- efa efb efe eff efo eft eo- eoa eob eoe eof eoo eot eta etb ete etf eto ett faa fab fae faf fao fat fba fbb fbe fbf fbo fbt fea feb fee fef feo fet ffa ffe fff ffo fft foa fob foe fof foo fot fta ftb fte ftf fto ftt oaa oab oae oaf oao oat ob- oba obb obe obf obo obt oea oeb oee oef oeo oet of- ofa ofb ofe off ofo oft oo- ooa oob oof ooo oot ot- ota otb ote otf oto ott taa tab tae taf tao tat tba tbb tbe tbf tbo tbt te- tea teb tee tef teo tet tfa tfb tfe tff tfo tft to- toa tob toe tof too tot tta ttb tte ttf tto ttt