-er a-a a-b a-i aaa aab aad aae aai aar aax ab- aba abb abd abe abi abr abx ad- ada adb add ade adi adr adx aea aeb aed aee aei aer aex ai- aia aib aid aie aii air aix ar- ara arb ard are ari arr arx ax- axa axe axi axr axx baa bab bad bae bai bar bax bba bbb bbd bbe bbi bbr bbx bda bdb bdd bde bdi bdr bdx be- bea beb bed bee bei ber bex bi- bia bib bid bie bii bir bix bra brb brd bre bri brr brx bxb bxd bxi bxx daa dab dad dae dai dar dax dba dbb dbd dbe dbi dbr dbx dda ddb ddd dde ddi ddr ddx de- dea deb ded dee dei der dex di- dia dib did die dii dir dix dra drb drd dre dri drr drx dxd dxi dxr dxx eaa eab ead eae eai ear eax eba ebb ebd ebe ebi ebr ebx ed- eda edb edd ede edi edr edx eea eeb eed eee eer eex eia eib eid eie eii eir eix era erb erd ere eri err ex- exa exd exe exi exr exx i-d ia- iaa iab iad iae iai iar iba ibb ibd ibe ibi ibr ibx ida idb idd ide idi idr idx ie- iea ied iee iei ier iex iia iib iid iie iii iir iix ir- ira irb ird ire iri irr irx ixe ixi ra- raa rab rad rae rai rar rax rba rbb rbd rbe rbi rbr rbx rda rdb rdd rde rdi rdr rdx re- rea reb red ree rei rer rex ria rib rid rie rii rir rix rra rrb rrd rri rrr rxr xaa xad xar xbe xbr xbx xda xdb xde xdi xdr xed xee xer xex xia xie xii xix xrd xrx xxi xxx