a-a a-b a-c aaa aab aac aaf aao aar aau ab- aba abb abc abf abo abr abu ac- aca acb acc acf aco acr acu af- afa afb afc aff afo afr afu aoa aob aoc aof aoo aor aou ar- ara arb arc arf aro arr aru au- aua aub auc auf auo aur b-u baa bab bac baf bao bar bau bba bbb bbc bbf bbo bbr bbu bca bcb bcc bcf bco bcr bcu bfa bfb bfc bff bfo bfr bfu boa bob boc bof boo bor bou bra brb brf bro brr bru bua bub buc buf buo bur buu c-- caa cab cac caf cao car cau cba cbb cbc cbf cbo cbr cbu cca ccb ccc ccf cco ccr ccu cfa cfb cfc cff cfo cfr cfu co- coa cob coc cof coo cor cou cra crb crc crf cro crr cru cua cub cuc cuf cuo cur cuu faa fab fac faf fao far fau fba fbb fbc fbf fbo fbr fbu fca fcb fcc fcf fco fcr fcu ffa ffc fff ffo ffr ffu foa fob foc fof foo for fou fra frb frc frf fro frr fru fua fub fuf fuo fur fuu oaa oab oac oaf oao oar oau ob- oba obb obc obf obo obr obu oc- oca ocb occ ocf oco ocr ocu of- ofa ofb ofc off ofo ofr ofu oo- ooa oob ooc oof ooo oor or- ora orb orc orf oro orr oru ou- oua ouc ouf ouo our ra- raa rab rac raf rao rar rau rba rbb rbc rbf rbo rbr rbu rca rcb rcc rcf rco rcr rcu rfa rfb rfc rff rfo rfr rfu roa rob roc rof roo ror rou rra rrb rrc rrf rrr rru rua rub ruc ruf ruo rur ruu ua- uaa uab uac uaf uao uar uau uba ubb ubc ubf ubo ubr ubu uca ucb ucc ucf uco ucr ucu ufa ufc uff ufo ufr ufu uoa uob uoc uoo uor ur- ura urb urc urf uro urr uru uua uuc uur uuu