-er a-a a-b a-i aaa aab aae aai aar aax ab- aba abb abe abi abr abx aea aeb aee aei aer aex ai- aia aib aie aii air aix ar- ara arb are ari arr arx ax- axa axe axi axr axx baa bab bae bai bar bax bba bbb bbe bbi bbr bbx be- bea beb bee bei ber bex bi- bia bib bie bii bir bix bra brb bre bri brr brx bxb bxi bxx eaa eab eae eai ear eax eba ebb ebe ebi ebr ebx eea eeb eee eer eex eia eib eie eii eir eix era erb ere eri err ex- exa exe exi exr exx ia- iaa iab iae iai iar iba ibb ibe ibi ibr ibx ie- iea iee iei ier iex iia iib iie iii iir iix ir- ira irb ire iri irr irx ixe ixi ra- raa rab rae rai rar rax rba rbb rbe rbi rbr rbx re- rea reb ree rei rer rex ria rib rie rii rir rix rra rrb rri rrr rxr xaa xar xbe xbr xbx xee xer xex xia xie xii xix xrx xxi xxx