-er a-a a-b aaa aab aae aak aar aax ab- aba abb abe abk abr abx aea aeb aee aek aer aex aka akb ake akk akr ar- ara arb are ark arr arx ax- axa axe axk axr axx baa bab bae bak bar bax bba bbb bbe bbk bbr bbx be- bea beb bee bek ber bex bka bkb bke bkk bkr bkx bra brb bre brk brr brx bxb bxx eaa eab eae eak ear eax eba ebb ebe ebk ebr ebx eea eeb eee eek eer eex eka ekb eke ekr era erb ere erk err ex- exa exe exr exx ka- kaa kab kae kak kar kax kba kbb kbe kbk kbr kbx ke- kea keb kee kek ker kex kkb kke kkk kkr kra krk krr ra- raa rab rae rak rar rax rba rbb rbe rbk rbr rbx re- rea reb ree rek rer rex rkb rke rkk rra rrb rrk rrr rxr xaa xak xar xbe xbr xbx xee xer xex xkb xke xrx xxx