b-u bbb bbi bbr bbs bbt bbu bi- bib bii bir bis bit biu brb bri brr brs brt bru bsb bsi bsr bss bst bsu btb bti btr bts btt btu bub bui bur bus but buu ibb ibi ibr ibs ibt ibu iib iii iir iis iit iiu ir- irb iri irr irs irt iru is- isb isi isr iss ist isu itb iti its itt itu iu- iub iui iur ius iut rbb rbi rbr rbs rbt rbu rib rii rir ris rit rrb rri rrr rrs rrt rru rsb rsi rsr rss rst rsu rtb rti rtr rts rtt rtu rub rui rur rus rut ruu sbb sbi sbr sbs sbt sbu sib sii sir sis sit siu sr- srb sri srr srs srt ss- ssb ssi ssr sss sst ssu stb sti str sts stt stu sub sui sur sus sut suu tbb tbi tbr tbs tbt tbu tib tii tir tis tit tiu trb tri trr trs trt tru tsb tsi tsr tss tst tsu ttb tti ttr tts ttt ttu tub tui tur tus tut tuu ubb ubi ubr ubs ubt ubu uib uii uir uis uit uiu ur- urb uri urr urs urt uru usb usi usr uss ust usu utb uti utr uts utt utu uur uus uut uuu