a-a a-b a-c aaa aab aac aan aao aau ab- aba abb abc abn abo abu ac- aca acb acc acn aco acu an- ana anb anc ann ano anu aoa aob aoc aon aoo aou au- aua aub auc aun auo b-u baa bab bac ban bao bau bba bbb bbc bbn bbo bbu bca bcb bcc bcn bco bcu bna bnb bnc bnn bno bnu boa bob boc bon boo bou bua bub buc bun buo buu c-- caa cab cac can cao cau cba cbb cbc cbn cbo cbu cca ccb ccc ccn cco ccu cn- cna cnb cnc cnn cno cnu co- coa cob coc con coo cou cua cub cuc cun cuo cuu naa nab nac nan nao nau nba nbb nbc nbn nbo nbu nca ncb ncc ncn nco ncu nna nnb nnc nnn nno nnu no- noa nob noc non noo nou nua nub nuc nun nuo nuu oaa oab oac oan oao oau ob- oba obb obc obn obo obu oc- oca ocb occ ocn oco ocu on- ona onb onc onn ono onu oo- ooa oob ooc oon ooo ou- oua ouc oun ouo ua- uaa uab uac uan uao uau uba ubb ubc ubn ubo ubu uca ucb ucc ucn uco ucu un- una unb unc unn uno unu uoa uob uoc uon uoo uua uuc uun uuu