-ol bbb bbl bbo bbr bbt blb bll blo blr blt bob bol boo bor bot brb brl bro brr brt btb btl bto btr btt lbb lbl lbo lbr lbt llb lll llo llr llt lob lol loo lor lot lrb lro lrr lrt ltb ltl lto ltr ltt ob- obb obl obo obr obt olb oll olo olt oo- oob ool ooo oor oot or- orb orl oro orr ort ot- otb otl oto otr ott rbb rbl rbo rbr rbt rll rlo rlr rlt rob rol roo ror rot rrb rrl rrr rrt rtb rtl rto rtr rtt tbb tbl tbo tbr tbt tll tlo tlr tlt to- tob tol too tor tot trb trl tro trr trt ttb ttl tto ttr ttt