bbb bbf bbr bbs bbt bfb bff bfr bfs bft brb brf brr brs brt bsb bsf bsr bss bst btb btf btr bts btt fbb fbf fbr fbs fbt fff ffr ffs fft frb frf frr frs frt fsb fsf fsr fss fst ftb ftf ftr fts ftt rbb rbf rbr rbs rbt rfb rff rfr rfs rft rrb rrf rrr rrs rrt rsb rsf rsr rss rst rtb rtf rtr rts rtt sbb sbf sbr sbs sbt sfb sff sfr sfs sft sr- srb srf srr srs srt ss- ssb ssf ssr sss sst stb stf str sts stt tbb tbf tbr tbs tbt tfb tff tfr tfs tft trb trf trr trs trt tsb tsf tsr tss tst ttb ttf ttr tts ttt