-er a-a a-b aaa aab aae aar aas aax ab- aba abb abe abr abs abx aea aeb aee aer aes aex ar- ara arb are arr ars arx as- asa asb ase asr ass asx ax- axa axe axr axs axx baa bab bae bar bas bax bba bbb bbe bbr bbs bbx be- bea beb bee ber bes bex bra brb bre brr brs brx bsa bsb bse bsr bss bsx bxb bxx eaa eab eae ear eas eax eba ebb ebe ebr ebs ebx eea eeb eee eer ees eex era erb ere err ers es- esa esb ese esr ess esx ex- exa exe exr exs exx ra- raa rab rae rar ras rax rba rbb rbe rbr rbs rbx re- rea reb ree rer res rex rra rrb rrr rrs rsa rsb rse rsr rss rsx rxr rxs saa sab sae sar sas sax sba sbb sbe sbr sbs sbx se- sea seb see ser ses sex sr- sra srb sre srr srs srx ss- ssa ssb sse ssr sss ssx sxs xaa xar xas xbe xbr xbx xee xer xes xex xrx xsa xsb xss xxx