bbb bbo bbr bbs bob boo bor bos bov brb bro brr brs brv bsb bso bsr bss bsv bvb bvo bvr bvs bvv ob- obb obo obr obs obv oo- oob ooo oor oos oov or- orb oro orr ors orv os- osb oso osr oss osv ov- ovb ovo ovs ovv rbb rbo rbr rbs rob roo ror ros rov rrb rrr rrs rsb rso rsr rss rsv rvb rvo rvr rvs rvv sbb sbo sbr sbs sbv sob soo sor sos sov sr- srb sro srr srs srv ss- ssb sso ssr sss ssv svb svo svr svs svv vbo vbr vbs vbv vob voo vor vos vov vrb vrr vrs vsb vso vsr vss vsv vvb vvo vvr vvs vvv