-er a-a a-b aaa aab aae aao aar aax ab- aba abb abe abo abr abx aea aeb aee aeo aer aex aoa aob aoe aoo aor aox ar- ara arb are aro arr arx ax- axa axe axo axr axx baa bab bae bao bar bax bba bbb bbe bbo bbr bbx be- bea beb bee beo ber bex boa bob boe boo bor box bra brb bre bro brr brx bxb bxo bxx eaa eab eae eao ear eax eba ebb ebe ebo ebr ebx eea eeb eee eeo eer eex eo- eoa eob eoe eoo eor era erb ere ero err ex- exa exe exo exr exx oaa oab oae oao oar oax ob- oba obb obe obo obr obx oea oeb oee oeo oer oex oo- ooa oob ooo oor oox or- ora orb ore oro orr orx ox- oxa oxb oxo oxx ra- raa rab rae rao rar rax rba rbb rbe rbo rbr rbx re- rea reb ree reo rer rex roa rob roe roo ror rox rra rrb rrr rxr xaa xar xbe xbr xbx xee xer xex xoa xoo xor xox xrx xxo xxx