a-a a-b aaa aab aag aao aar ab- aba abb abg abo abr ag- aga agb agg ago agr aoa aob aog aoo aor ar- ara arb arg aro arr baa bab bag bao bar bba bbb bbg bbo bbr bga bgb bgg bgo bgr boa bob bog boo bor bra brb brg bro brr gaa gab gag gao gar gba gbg gbo gbr gga ggb ggg ggo ggr goa gob gog goo gor gra grb grg gro grr oaa oab oag oao oar ob- oba obb obg obo obr oga ogg ogo oo- ooa oob oog ooo oor or- ora orb org oro orr ra- raa rab rag rao rar rba rbb rbg rbo rbr rga rgb rgg rgo rgr roa rob rog roo ror rra rrb rrg rrr