-er bbb bbe bbm bbo bbr bbx be- beb bee bem beo ber bex bmb bme bmm bmo bmr bmx bob boe bom boo bor box brb bre brm bro brr brx bxb bxm bxo bxx ebb ebe ebm ebo ebr ebx eeb eee eem eeo eer eex em- emb eme emm emo emr emx eo- eob eoe eom eoo eor erb ere erm ero err ex- exe exo exr exx m-o m-r mbb mbe mbm mbo mbr mbx meb mee mem meo mer mex mmb mme mmm mmo mmr mmx mob moe mom moo mor mox mrb mre mrm mro mrr mrx mxr ob- obb obe obm obo obr obx oeb oee oem oeo oer oex om- omb ome omm omo omr omx oo- oob oom ooo oor oox or- orb ore orm oro orr orx ox- oxb oxo oxx rbb rbe rbm rbo rbr rbx re- reb ree rem reo rer rex rmb rme rmm rmo rmr rmx rob roe rom roo ror rox rrb rrm rrr rxr xbe xbr xbx xee xem xer xex xmm xmo xmr xmx xom xoo xor xox xrx xxo xxx