a-a a-b a-c aaa aab aac aao aar aau ab- aba abb abc abo abr abu ac- aca acb acc aco acr acu aoa aob aoc aoo aor aou ar- ara arb arc aro arr aru au- aua aub auc auo aur b-u baa bab bac bao bar bau bba bbb bbc bbo bbr bbu bca bcb bcc bco bcr bcu boa bob boc boo bor bou bra brb bro brr bru bua bub buc buo bur buu c-- caa cab cac cao car cau cba cbb cbc cbo cbr cbu cca ccb ccc cco ccr ccu co- coa cob coc coo cor cou cra crb crc cro crr cru cua cub cuc cuo cur cuu oaa oab oac oao oar oau ob- oba obb obc obo obr obu oc- oca ocb occ oco ocr ocu oo- ooa oob ooc ooo oor or- ora orb orc oro orr oru ou- oua ouc ouo our ra- raa rab rac rao rar rau rba rbb rbc rbo rbr rbu rca rcb rcc rco rcr rcu roa rob roc roo ror rou rra rrb rrc rrr rru rua rub ruc ruo rur ruu ua- uaa uab uac uao uar uau uba ubb ubc ubo ubr ubu uca ucb ucc uco ucr ucu uoa uob uoc uoo uor ur- ura urb urc uro urr uru uua uuc uur uuu