a-a a-b a-c aaa aab aac aao aau ab- aba abb abc abo abu ac- aca acb acc aco acu aoa aob aoc aoo aou au- aua aub auc auo b-u baa bab bac bao bau bba bbb bbc bbo bbu bca bcb bcc bco bcu boa bob boc boo bou bua bub buc buo buu c-- caa cab cac cao cau cba cbb cbc cbo cbu cca ccb ccc cco ccu co- coa cob coc coo cou cua cub cuc cuo cuu oaa oab oac oao oau ob- oba obb obc obo obu oc- oca ocb occ oco ocu oo- ooa oob ooc ooo ou- oua ouc ouo ua- uaa uab uac uao uau uba ubb ubc ubo ubu uca ucb ucc uco ucu uoa uob uoc uoo uua uuc uuu