bbb bbo bbs bbt bbx bob boo bos bot box bsb bso bss bst bsx btb bto bts btt btx bxb bxo bxx ob- obb obo obs obt obx oo- oob ooo oos oot oox os- osb oso oss ost osx ot- otb oto ots ott ox- oxb oxo oxt oxx sbb sbo sbs sbt sbx sob soo sos sot sox ss- ssb sso sss sst ssx stb sto sts stt stx sxs sxt t-x tbb tbo tbs tbt to- tob too tos tot tox tsb tso tss tst tsx ttb tto tts ttt ttx txs txt xbx xoo xos xot xox xsb xss xst xts xtx xxo xxx