-er a-a a-b aaa aab aae aao aar aas aax ab- aba abb abe abo abr abs abx aea aeb aee aeo aer aes aex aoa aob aoe aoo aor aos aox ar- ara arb are aro arr ars arx as- asa asb ase aso asr ass asx ax- axa axe axo axr axs axx baa bab bae bao bar bas bax bba bbb bbe bbo bbr bbs bbx be- bea beb bee beo ber bes bex boa bob boe boo bor bos box bra brb bre bro brr brs brx bsa bsb bse bso bsr bss bsx bxb bxo bxx eaa eab eae eao ear eas eax eba ebb ebe ebo ebr ebs ebx eea eeb eee eeo eer ees eex eo- eoa eob eoe eoo eor eos era erb ere ero err ers es- esa esb ese eso esr ess esx ex- exa exe exo exr exs exx oaa oab oae oao oar oas oax ob- oba obb obe obo obr obs obx oea oeb oee oeo oer oes oex oo- ooa oob ooo oor oos oox or- ora orb ore oro orr ors orx os- osa osb ose oso osr oss osx ox- oxa oxb oxo oxx ra- raa rab rae rao rar ras rax rba rbb rbe rbo rbr rbs rbx re- rea reb ree reo rer res rex roa rob roe roo ror ros rox rra rrb rrr rrs rsa rsb rse rso rsr rss rsx rxr rxs saa sab sae sao sar sas sax sba sbb sbe sbo sbr sbs sbx se- sea seb see seo ser ses sex soa sob soe soo sor sos sox sr- sra srb sre sro srr srs srx ss- ssa ssb sse sso ssr sss ssx sxs xaa xar xas xbe xbr xbx xee xer xes xex xoa xoo xor xos xox xrx xsa xsb xss xxo xxx