a-a a-b a-i aaa aab aai aao aax ab- aba abb abi abo abx ai- aia aib aii aio aix aoa aob aoi aoo aox ax- axa axi axo axx baa bab bai bao bax bba bbb bbi bbo bbx bi- bia bib bii bio bix boa bob boi boo box bxb bxi bxo bxx ia- iaa iab iai iao iba ibb ibi ibo ibx iia iib iii iio iix io- ioa iob ioi ioo ixi o-i oaa oab oai oao oax ob- oba obb obi obo obx oia oib oii oio oo- ooa oob ooi ooo oox ox- oxa oxb oxi oxo oxx xaa xbx xia xii xio xix xoa xoi xoo xox xxi xxo xxx