-er a-a a-b a-t aaa aab aae aar aat aax ab- aba abb abe abr abt abx aea aeb aee aer aet aex ar- ara arb are arr art arx at- ata atb ate atr att atx ax- axa axe axr axt axx baa bab bae bar bat bax bba bbb bbe bbr bbt bbx be- bea beb bee ber bet bex bra brb bre brr brt brx bta btb bte btr btt btx bxb bxx eaa eab eae ear eat eax eba ebb ebe ebr ebt ebx eea eeb eee eer eet eex era erb ere err ert eta etb ete etr ett etx ex- exa exe exr ext exx ra- raa rab rae rar rat rax rba rbb rbe rbr rbt rbx re- rea reb ree rer ret rex rra rrb rrr rrt rta rtb rte rtr rtt rtx rxr t-x taa tab tae tar tat tax tba tbb tbe tbr tbt te- tea teb tee ter tet tex tra trb tre trr trt trx tta ttb tte ttr ttt ttx txe txt xaa xar xat xbe xbr xbx xee xer xet xex xrt xrx xtr xtx xxx