a-a a-b aaa aab aad aan aao ab- aba abb abd abn abo ad- ada adb add adn ado an- ana anb and ann ano aoa aob aod aon aoo baa bab bad ban bao bba bbb bbd bbn bbo bda bdb bdd bdo bna bnb bnd bnn bno boa bob bod bon boo daa dab dad dan dao dba dbb dbd dbn dbo dda ddb ddd ddn ddo dna dnb dnd dnn dno doa dob dod don doo naa nab nad nan nao nba nbb nbd nbn nbo nda ndb ndd ndn ndo nna nnb nnn nno no- noa nob nod non noo oaa oab oad oan oao ob- oba obb obd obn obo oda odb odd odn odo on- ona onb ond onn ono oo- ooa oob ood oon ooo