a-a a-b aaa aab aad aao aau ab- aba abb abd abo abu ad- ada adb add ado adu aoa aob aod aoo aou au- aua aub aud auo b-u baa bab bad bao bau bba bbb bbd bbo bbu bda bdb bdd bdo bdu boa bob bod boo bou bua bub bud buo buu daa dab dad dao dau dba dbb dbd dbo dbu dda ddb ddd ddo ddu doa dob dod doo dou dua dub dud duo oaa oab oad oao oau ob- oba obb obd obo obu oda odb odd odo odu oo- ooa oob ood ooo ou- oua oud ouo ua- uaa uab uad uao uau uba ubb ubo ubu uda udb udd udo udu uoa uob uod uoo uua uuu