-er b-p bbb bbe bbo bbp bbr bbs bbx be- beb bee beo bep ber bes bex bob boe boo bop bor bos box bpb bpe bpo bpp bpr bps bpx brb bre bro brp brr brs brx bsb bse bso bsp bsr bss bsx bxb bxo bxx ebb ebe ebo ebp ebr ebs ebx eeb eee eeo eep eer ees eex eo- eob eoe eoo eop eor eos ep- epb epe epo epp epr eps epx erb ere ero erp err ers es- esb ese eso esp esr ess esx ex- exe exo exp exr exs exx ob- obb obe obo obp obr obs obx oeb oee oeo oep oer oes oex oo- oob ooo oop oor oos oox op- opb ope opo opp opr ops opx or- orb ore oro orp orr ors orx os- osb ose oso osp osr oss osx ox- oxb oxo oxx p-p pbb pbe pbo pbp pbr pbs pbx peb pee peo pep per pes pex pob poe poo pop por pos pox ppb ppe ppo ppp ppr pps ppx prb pre pro prp prr prs prx ps- psb pse pso psp psr pss psx pxe pxr pxs rbb rbe rbo rbp rbr rbs rbx re- reb ree reo rep rer res rex rob roe roo rop ror ros rox rpb rpe rpo rpp rpr rps rpx rrb rrp rrr rrs rsb rse rso rsp rsr rss rsx rxp rxr rxs sbb sbe sbo sbp sbr sbs sbx se- seb see seo sep ser ses sex sob soe soo sop sor sos sox spb spe spo spp spr sps spx sr- srb sre sro srp srr srs srx ss- ssb sse sso ssp ssr sss ssx sxs xbe xbr xbx xee xep xer xes xex xoo xop xor xos xox xpb xpe xpo xpp xps xrx xsb xsp xss xxo xxp xxx