-er bbb bbc bbe bbr bbs bcb bcc bce bcr bcs be- beb bec bee ber bes brb bre brr brs bsb bsc bse bsr bss c-- cbb cbc cbe cbr cbs ccb ccc cce ccr ccs ce- ceb cec cee cer ces crb crc cre crr crs csb csc cse csr css ebb ebc ebe ebr ebs ec- ecb ecc ece ecr ecs eeb eec eee eer ees erb erc ere err ers es- esb esc ese esr ess rbb rbc rbe rbr rbs rcb rcc rce rcr rcs re- reb rec ree rer res rrb rrc rrr rrs rsb rsc rse rsr rss sbb sbc sbe sbr sbs scb scc sce scr scs se- seb sec see ser ses sr- srb src sre srr srs ss- ssb ssc sse ssr sss