-er a-a a-b aaa aab aae aaf aao aar aax ab- aba abb abe abf abo abr abx aea aeb aee aef aeo aer aex af- afa afb afe aff afo afr afx aoa aob aoe aof aoo aor aox ar- ara arb are arf aro arr arx ax- axa axe axo axr axx baa bab bae baf bao bar bax bba bbb bbe bbf bbo bbr bbx be- bea beb bee bef beo ber bex bfa bfb bfe bff bfo bfr bfx boa bob boe bof boo bor box bra brb bre brf bro brr brx bxb bxo bxx eaa eab eae eaf eao ear eax eba ebb ebe ebf ebo ebr ebx eea eeb eee eef eeo eer eex ef- efa efb efe eff efo efr efx eo- eoa eob eoe eof eoo eor era erb ere erf ero err ex- exa exe exo exr exx faa fab fae faf fao far fax fba fbb fbe fbf fbo fbr fbx fea feb fee fef feo fer fex ffa ffe fff ffo ffr ffx foa fob foe fof foo for fox fra frb fre frf fro frr fxe fxr fxx oaa oab oae oaf oao oar oax ob- oba obb obe obf obo obr obx oea oeb oee oef oeo oer oex of- ofa ofb ofe off ofo ofr ofx oo- ooa oob oof ooo oor oox or- ora orb ore orf oro orr orx ox- oxa oxb oxf oxo oxx ra- raa rab rae raf rao rar rax rba rbb rbe rbf rbo rbr rbx re- rea reb ree ref reo rer rex rfa rfb rfe rff rfo rfr roa rob roe rof roo ror rox rra rrb rrf rrr rxr xaa xaf xar xbe xbr xbx xee xer xex xfa xfe xfx xoa xof xoo xor xox xrf xrx xxo xxx