a-a a-b aaa aab aad aao aax ab- aba abb abd abo abx ad- ada adb add ado adx aoa aob aod aoo aox ax- axa axo axx baa bab bad bao bax bba bbb bbd bbo bbx bda bdb bdd bdo bdx boa bob bod boo box bxb bxd bxo bxx daa dab dad dao dax dba dbb dbd dbo dbx dda ddb ddd ddo ddx doa dob dod doo dox dxd dxo dxx oaa oab oad oao oax ob- oba obb obd obo obx oda odb odd odo oo- ooa oob ood ooo oox ox- oxa oxb oxo oxx xaa xad xbx xda xdb xoa xod xoo xox xxo xxx