bbb bbc bbd bbk bbo bcb bcc bcd bck bco bdb bdc bdd bdk bdo bkb bkc bkk bko bob boc bod bok boo c-- cbb cbc cbd cbk cbo ccb ccc ccd cck cco cdb cdc cdd cdk cdo ckb ckc ckd cko co- cob coc cod cok coo dbb dbc dbd dbk dbo dcb dcc dcd dck dco ddb ddc ddd ddk ddo dkb dkc dkk dko dob doc dod dok doo kbb kbc kbd kbk kbo kcb kcc kcd kck kdb kdc kdk kdo kkb kkc kkk kob koc kod kok koo ob- obb obc obd obk obo oc- ocb occ ocd ock oco odb odc odd odo okb okc okd okk oko oo- oob ooc ood ook ooo