-er a-a a-b aaa aab aae aag aao aar ab- aba abb abe abg abo abr aea aeb aee aeg aeo aer ag- aga agb age agg ago agr aoa aob aoe aog aoo aor ar- ara arb are arg aro arr baa bab bae bag bao bar bba bbb bbe bbg bbo bbr be- bea beb bee beg beo ber bga bgb bge bgg bgo bgr boa bob boe bog boo bor bra brb bre brg bro brr eaa eab eae eag eao ear eba ebb ebe ebg ebo ebr eea eeb eee eeg eeo eer ega egb ege egg ego egr eo- eoa eob eoe eog eoo eor era erb ere erg ero err gaa gab gae gag gao gar gba gbe gbg gbo gbr ge- gea geb gee geg geo ger gga ggb ggg ggo ggr goa gob goe gog goo gor gra grb gre grg gro grr oaa oab oae oag oao oar ob- oba obb obe obg obo obr oea oeb oee oeg oeo oer oga oge ogg ogo oo- ooa oob oog ooo oor or- ora orb ore org oro orr ra- raa rab rae rag rao rar rba rbb rbe rbg rbo rbr re- rea reb ree reg reo rer rga rgb rge rgg rgo rgr roa rob roe rog roo ror rra rrb rrg rrr