-er bbb bbe bbr bbs bbt bbx be- beb bee ber bes bet bex brb bre brr brs brt brx bsb bse bsr bss bst bsx btb bte btr bts btt btx bxb bxx ebb ebe ebr ebs ebt ebx eeb eee eer ees eet eex erb ere err ers ert es- esb ese esr ess est esx etb ete etr ets ett etx ex- exe exr exs ext exx rbb rbe rbr rbs rbt rbx re- reb ree rer res ret rex rrb rrr rrs rrt rsb rse rsr rss rst rsx rtb rte rtr rts rtt rtx rxr rxs sbb sbe sbr sbs sbt sbx se- seb see ser ses set sex sr- srb sre srr srs srt srx ss- ssb sse ssr sss sst ssx stb ste str sts stt stx sxs sxt t-x tbb tbe tbr tbs tbt te- teb tee ter tes tet tex trb tre trr trs trt trx tsb tse tsr tss tst tsx ttb tte ttr tts ttt ttx txe txs txt xbe xbr xbx xee xer xes xet xex xrt xrx xsb xss xst xtr xts xtx xxx