b-u bbb bbf bbo bbr bbu bfb bff bfo bfr bfu bob bof boo bor bou brb brf bro brr bru bub buf buo bur buu fbb fbf fbo fbr fbu fff ffo ffr ffu fob fof foo for fou frb frf fro frr fru fub fuf fuo fur fuu ob- obb obf obo obr obu of- ofb off ofo ofr ofu oo- oob oof ooo oor or- orb orf oro orr oru ou- ouf ouo our rbb rbf rbo rbr rbu rfb rff rfo rfr rfu rob rof roo ror rou rrb rrf rrr rru rub ruf ruo rur ruu ubb ubf ubo ubr ubu uff ufo ufr ufu uob uoo uor ur- urb urf uro urr uru uur uuu