bbb bbm bbo bbr bbx bmb bmm bmo bmr bmx bob bom boo bor box brb brm bro brr brx bxb bxm bxo bxx m-o m-r mbb mbm mbo mbr mbx mmb mmm mmo mmr mmx mob mom moo mor mox mrb mrm mro mrr mrx mxr ob- obb obm obo obr obx om- omb omm omo omr omx oo- oob oom ooo oor oox or- orb orm oro orr orx ox- oxb oxo oxx rbb rbm rbo rbr rbx rmb rmm rmo rmr rmx rob rom roo ror rox rrb rrm rrr rxr xbr xbx xmm xmo xmr xmx xom xoo xor xox xrx xxo xxx