bbb bbc bbd bbo bbr bcb bcc bcd bco bcr bdb bdc bdd bdo bdr bob boc bod boo bor brb brd bro brr c-- cbb cbc cbd cbo cbr ccb ccc ccd cco ccr cdb cdc cdd cdo cdr co- cob coc cod coo cor crb crc crd cro crr dbb dbc dbd dbo dbr dcb dcc dcd dco dcr ddb ddc ddd ddo ddr dob doc dod doo dor drb drc drd dro drr ob- obb obc obd obo obr oc- ocb occ ocd oco ocr odb odc odd odo odr oo- oob ooc ood ooo oor or- orb orc ord oro orr rbb rbc rbd rbo rbr rcb rcc rcd rco rcr rdb rdc rdd rdo rdr rob roc rod roo ror rrb rrc rrd rrr