bbb bbi bbo bbr bbs bbt bi- bib bii bio bir bis bit bob boi boo bor bos bot brb bri bro brr brs brt bsb bsi bso bsr bss bst btb bti bto btr bts btt ibb ibi ibo ibr ibs ibt iib iii iio iir iis iit io- iob ioi ioo ior ios iot ir- irb iri iro irr irs irt is- isb isi iso isr iss ist itb iti ito its itt o-i ob- obb obi obo obr obs obt oib oii oio oir ois oit oo- oob ooi ooo oor oos oot or- orb ori oro orr ors ort os- osb osi oso osr oss ost ot- otb oti oto otr ots ott rbb rbi rbo rbr rbs rbt rib rii rio rir ris rit rob roi roo ror ros rot rrb rri rrr rrs rrt rsb rsi rso rsr rss rst rtb rti rto rtr rts rtt sbb sbi sbo sbr sbs sbt sib sii sio sir sis sit sob soi soo sor sos sot sr- srb sri sro srr srs srt ss- ssb ssi sso ssr sss sst stb sti sto str sts stt tbb tbi tbo tbr tbs tbt tib tii tio tir tis tit to- tob toi too tor tos tot trb tri tro trr trs trt tsb tsi tso tsr tss tst ttb tti tto ttr tts ttt