-er a-a a-b aaa aab aae aaf aao aar aas aax ab- aba abb abe abf abo abr abs abx aea aeb aee aef aeo aer aes aex af- afa afb afe aff afo afr afs afx aoa aob aoe aof aoo aor aos aox ar- ara arb are arf aro arr ars arx as- asa asb ase asf aso asr ass asx ax- axa axe axo axr axs axx baa bab bae baf bao bar bas bax bba bbb bbe bbf bbo bbr bbs bbx be- bea beb bee bef beo ber bes bex bfa bfb bfe bff bfo bfr bfs bfx boa bob boe bof boo bor bos box bra brb bre brf bro brr brs brx bsa bsb bse bsf bso bsr bss bsx bxb bxo bxx eaa eab eae eaf eao ear eas eax eba ebb ebe ebf ebo ebr ebs ebx eea eeb eee eef eeo eer ees eex ef- efa efb efe eff efo efr efs efx eo- eoa eob eoe eof eoo eor eos era erb ere erf ero err ers es- esa esb ese esf eso esr ess esx ex- exa exe exo exr exs exx faa fab fae faf fao far fas fax fba fbb fbe fbf fbo fbr fbs fbx fea feb fee fef feo fer fes fex ffa ffe fff ffo ffr ffs ffx foa fob foe fof foo for fos fox fra frb fre frf fro frr frs fsa fsb fse fsf fso fsr fss fsx fxe fxr fxs fxx oaa oab oae oaf oao oar oas oax ob- oba obb obe obf obo obr obs obx oea oeb oee oef oeo oer oes oex of- ofa ofb ofe off ofo ofr ofs ofx oo- ooa oob oof ooo oor oos oox or- ora orb ore orf oro orr ors orx os- osa osb ose osf oso osr oss osx ox- oxa oxb oxf oxo oxx ra- raa rab rae raf rao rar ras rax rba rbb rbe rbf rbo rbr rbs rbx re- rea reb ree ref reo rer res rex rfa rfb rfe rff rfo rfr rfs roa rob roe rof roo ror ros rox rra rrb rrf rrr rrs rsa rsb rse rsf rso rsr rss rsx rxr rxs saa sab sae saf sao sar sas sax sba sbb sbe sbf sbo sbr sbs sbx se- sea seb see sef seo ser ses sex sfa sfb sfe sff sfo sfr sfs sfx soa sob soe sof soo sor sos sox sr- sra srb sre srf sro srr srs srx ss- ssa ssb sse ssf sso ssr sss ssx sxs xaa xaf xar xas xbe xbr xbx xee xer xes xex xfa xfe xfs xfx xoa xof xoo xor xos xox xrf xrx xsa xsb xss xxo xxx