-er bbb bbe bbo bbr bbt be- beb bee beo ber bet bob boe boo bor bot brb bre bro brr brt btb bte bto btr btt ebb ebe ebo ebr ebt eeb eee eeo eer eet eo- eob eoe eoo eor eot erb ere ero err ert etb ete eto etr ett ob- obb obe obo obr obt oeb oee oeo oer oet oo- oob ooo oor oot or- orb ore oro orr ort ot- otb ote oto otr ott rbb rbe rbo rbr rbt re- reb ree reo rer ret rob roe roo ror rot rrb rrr rrt rtb rte rto rtr rtt tbb tbe tbo tbr tbt te- teb tee teo ter tet to- tob toe too tor tot trb tre tro trr trt ttb tte tto ttr ttt