bbb bbc bbo bbs bbt bcb bcc bco bcs bct bob boc boo bos bot bsb bsc bso bss bst btb btc bto bts btt c-- cbb cbc cbo cbs cbt ccb ccc cco ccs cct co- cob coc coo cos cot csb csc cso css cst ctb ctc cto cts ctt ob- obb obc obo obs obt oc- ocb occ oco ocs oct oo- oob ooc ooo oos oot os- osb osc oso oss ost ot- otb otc oto ots ott sbb sbc sbo sbs sbt scb scc sco scs sct sob soc soo sos sot ss- ssb ssc sso sss sst stb stc sto sts stt tbb tbc tbo tbs tbt tcb tcc tco tcs tct to- tob toc too tos tot tsb tsc tso tss tst ttb ttc tto tts ttt