a-a a-b aaa aab aaf aag aao aar ab- aba abb abf abg abo abr af- afa afb aff afg afo afr ag- aga agb agf agg ago agr aoa aob aof aog aoo aor ar- ara arb arf arg aro arr baa bab baf bag bao bar bba bbb bbf bbg bbo bbr bfa bfb bff bfg bfo bfr bga bgb bgf bgg bgo bgr boa bob bof bog boo bor bra brb brf brg bro brr faa fab faf fag fao far fba fbb fbf fbg fbo fbr ffa fff ffg ffo ffr fga fgb fgf fgg fgr foa fob fof fog foo for fra frb frf frg fro frr gaa gab gaf gag gao gar gba gbf gbg gbo gbr gfa gfb gff gfo gfr gga ggb ggg ggo ggr goa gob gof gog goo gor gra grb grf grg gro grr oaa oab oaf oag oao oar ob- oba obb obf obg obo obr of- ofa ofb off ofg ofo ofr oga ogf ogg ogo oo- ooa oob oof oog ooo oor or- ora orb orf org oro orr ra- raa rab raf rag rao rar rba rbb rbf rbg rbo rbr rfa rfb rff rfg rfo rfr rga rgb rgf rgg rgo rgr roa rob rof rog roo ror rra rrb rrf rrg rrr