bbb bbm bbo bbr bbt bmb bmm bmo bmr bmt bob bom boo bor bot brb brm bro brr brt btb btm bto btr btt m-o m-r mbb mbm mbo mbr mbt mmb mmm mmo mmr mmt mob mom moo mor mot mrb mrm mro mrr mrt mtb mtm mto mtr mtt ob- obb obm obo obr obt om- omb omm omo omr omt oo- oob oom ooo oor oot or- orb orm oro orr ort ot- otb otm oto otr ott rbb rbm rbo rbr rbt rmb rmm rmo rmr rmt rob rom roo ror rot rrb rrm rrr rrt rtb rtm rto rtr rtt tbb tbm tbo tbr tbt tmb tmm tmo tmr tmt to- tob tom too tor tot trb trm tro trr trt ttb ttm tto ttr ttt