-er bbb bbc bbe bbr bbt bcb bcc bce bcr bct be- beb bec bee ber bet brb bre brr brt btb btc bte btr btt c-- cbb cbc cbe cbr cbt ccb ccc cce ccr cct ce- ceb cec cee cer cet crb crc cre crr crt ctb ctc cte ctr ctt ebb ebc ebe ebr ebt ec- ecb ecc ece ecr ect eeb eec eee eer eet erb erc ere err ert etb etc ete etr ett rbb rbc rbe rbr rbt rcb rcc rce rcr rct re- reb rec ree rer ret rrb rrc rrr rrt rtb rtc rte rtr rtt tbb tbc tbe tbr tbt tcb tcc tce tcr tct te- teb tec tee ter tet trb trc tre trr trt ttb ttc tte ttr ttt