a-a a-b aaa aab aan aao aax ab- aba abb abn abo abx an- ana anb ann ano anx aoa aob aon aoo aox ax- axa axn axo axx baa bab ban bao bax bba bbb bbn bbo bbx bna bnb bnn bno bnx boa bob bon boo box bxb bxn bxo bxx naa nab nan nao nax nba nbb nbn nbo nbx nna nnb nnn nno no- noa nob non noo nox oaa oab oan oao oax ob- oba obb obn obo obx on- ona onb onn ono onx oo- ooa oob oon ooo oox ox- oxa oxb oxn oxo oxx xaa xan xbx xna xno xoa xon xoo xox xxo xxx