-er bbb bbc bbe bbo bbr bbt bcb bcc bce bco bcr bct be- beb bec bee beo ber bet bob boc boe boo bor bot brb bre bro brr brt btb btc bte bto btr btt c-- cbb cbc cbe cbo cbr cbt ccb ccc cce cco ccr cct ce- ceb cec cee ceo cer cet co- cob coc coe coo cor cot crb crc cre cro crr crt ctb ctc cte cto ctr ctt ebb ebc ebe ebo ebr ebt ec- ecb ecc ece eco ecr ect eeb eec eee eeo eer eet eo- eob eoc eoe eoo eor eot erb erc ere ero err ert etb etc ete eto etr ett ob- obb obc obe obo obr obt oc- ocb occ oco ocr oct oeb oec oee oeo oer oet oo- oob ooc ooo oor oot or- orb orc ore oro orr ort ot- otb otc ote oto otr ott rbb rbc rbe rbo rbr rbt rcb rcc rce rco rcr rct re- reb rec ree reo rer ret rob roc roe roo ror rot rrb rrc rrr rrt rtb rtc rte rto rtr rtt tbb tbc tbe tbo tbr tbt tcb tcc tce tco tcr tct te- teb tec tee teo ter tet to- tob toc toe too tor tot trb trc tre tro trr trt ttb ttc tte tto ttr ttt