-er a-a a-b a-i a-t aaa aab aae aai aar aat aax ab- aba abb abe abi abr abt abx aea aeb aee aei aer aet aex ai- aia aib aie aii air ait aix ar- ara arb are ari arr art arx at- ata atb ate ati atr att atx ax- axa axe axi axr axt axx baa bab bae bai bar bat bax bba bbb bbe bbi bbr bbt bbx be- bea beb bee bei ber bet bex bi- bia bib bie bii bir bit bix bra brb bre bri brr brt brx bta btb bte bti btr btt btx bxb bxi bxx eaa eab eae eai ear eat eax eba ebb ebe ebi ebr ebt ebx eea eeb eee eer eet eex eia eib eie eii eir eit eix era erb ere eri err ert eta etb ete eti etr ett etx ex- exa exe exi exr ext exx ia- iaa iab iae iai iar iat iba ibb ibe ibi ibr ibt ibx ie- iea iee iei ier iet iex iia iib iie iii iir iit iix ir- ira irb ire iri irr irt irx ita itb ite iti itt itx ixe ixi ra- raa rab rae rai rar rat rax rba rbb rbe rbi rbr rbt rbx re- rea reb ree rei rer ret rex ria rib rie rii rir rit rix rra rrb rri rrr rrt rta rtb rte rti rtr rtt rtx rxr t-x taa tab tae tai tar tat tax tba tbb tbe tbi tbr tbt te- tea teb tee tei ter tet tex tia tib tie tii tir tit tix tra trb tre tri trr trt trx tta ttb tte tti ttr ttt ttx txe txi txt xaa xar xat xbe xbr xbx xee xer xet xex xia xie xii xit xix xrt xrx xti xtr xtx xxi xxx