bbb bbi bbo bbs bbt bi- bib bii bio bis bit bob boi boo bos bot bsb bsi bso bss bst btb bti bto bts btt ibb ibi ibo ibs ibt iib iii iio iis iit io- iob ioi ioo ios iot is- isb isi iso iss ist itb iti ito its itt o-i ob- obb obi obo obs obt oib oii oio ois oit oo- oob ooi ooo oos oot os- osb osi oso oss ost ot- otb oti oto ots ott sbb sbi sbo sbs sbt sib sii sio sis sit sob soi soo sos sot ss- ssb ssi sso sss sst stb sti sto sts stt tbb tbi tbo tbs tbt tib tii tio tis tit to- tob toi too tos tot tsb tsi tso tss tst ttb tti tto tts ttt