a-a a-b aaa aab aae aaf aag aao ab- aba abb abe abf abg abo aea aeb aee aef aeg aeo af- afa afb afe aff afg afo ag- aga agb age agf agg ago aoa aob aoe aof aog aoo baa bab bae baf bag bao bba bbb bbe bbf bbg bbo be- bea beb bee bef beg beo bfa bfb bfe bff bfg bfo bga bgb bge bgf bgg bgo boa bob boe bof bog boo eaa eab eae eaf eag eao eba ebb ebe ebf ebg ebo eea eeb eee eef eeg eeo ef- efa efb efe eff efg efo ega egb ege egf egg ego eo- eoa eob eoe eof eog eoo faa fab fae faf fag fao fba fbb fbe fbf fbg fbo fea feb fee fef feg feo ffa ffe fff ffg ffo fga fgb fge fgf fgg foa fob foe fof fog foo gaa gab gae gaf gag gao gba gbe gbf gbg gbo ge- gea geb gee gef geg geo gfa gfb gfe gff gfo gga ggb ggg ggo goa gob goe gof gog goo oaa oab oae oaf oag oao ob- oba obb obe obf obg obo oea oeb oee oef oeg oeo of- ofa ofb ofe off ofg ofo oga oge ogf ogg ogo oo- ooa oob oof oog ooo