bbb bbc bbn bbo bbs bcb bcc bcn bco bcs bnb bnc bnn bno bns bob boc bon boo bos bsb bsc bsn bso bss c-- cbb cbc cbn cbo cbs ccb ccc ccn cco ccs cn- cnb cnc cnn cno cns co- cob coc con coo cos csb csc csn cso css nbb nbc nbn nbo nbs ncb ncc ncn nco ncs nnb nnc nnn nno nns no- nob noc non noo nos nsb nsc nsn nso nss ob- obb obc obn obo obs oc- ocb occ ocn oco ocs on- onb onc onn ono ons oo- oob ooc oon ooo oos os- osb osc osn oso oss sbb sbc sbn sbo sbs scb scc scn sco scs snb snc snn sno sns sob soc son soo sos ss- ssb ssc ssn sso sss