a-a a-b a-i aaa aab aae aai aax ab- aba abb abe abi abx aea aeb aee aei aex ai- aia aib aie aii aix ax- axa axe axi axx baa bab bae bai bax bba bbb bbe bbi bbx be- bea beb bee bei bex bi- bia bib bie bii bix bxb bxi bxx eaa eab eae eai eax eba ebb ebe ebi ebx eea eeb eee eex eia eib eie eii eix ex- exa exe exi exx ia- iaa iab iae iai iba ibb ibe ibi ibx ie- iea iee iei iex iia iib iie iii iix ixe ixi xaa xbe xbx xee xex xia xie xii xix xxi xxx