b-u bbb bbs bbt bbu bby bsb bss bst bsu bsy btb bts btt btu bty bub bus but buu buy by- bys byt byu sbb sbs sbt sbu sby ss- ssb sss sst ssu stb sts stt stu sty sub sus sut suu suy sy- syb sys syt syu tbb tbs tbt tbu tsb tss tst tsu tsy ttb tts ttt ttu tty tub tus tut tuu tuy tys tyt ubb ubs ubt ubu uby usb uss ust usu utb uts utt utu uty uus uut uuu uys uyu ybs yby ysb yss yst ysu ysy yts ytt ytu yus yut yuu yuy yyb yys yyt yyu yyy