-er bbb bbc bbe bbg bbo bbr bcb bcc bce bcg bco bcr be- beb bec bee beg beo ber bgb bgc bge bgg bgo bgr bob boc boe bog boo bor brb bre brg bro brr c-- cbb cbc cbe cbg cbo cbr ccb ccc cce ccg cco ccr ce- ceb cec cee ceg ceo cer cgb cgc cge cgg cgo cgr co- cob coc coe cog coo cor crb crc cre crg cro crr ebb ebc ebe ebg ebo ebr ec- ecb ecc ece ecg eco ecr eeb eec eee eeg eeo eer egb egc ege egg ego egr eo- eob eoc eoe eog eoo eor erb erc ere erg ero err gbc gbe gbg gbo gbr gcb gcc gce gcg gco gcr ge- geb gec gee geg geo ger ggb ggc ggg ggo ggr gob goc goe gog goo gor grb grc gre grg gro grr ob- obb obc obe obg obo obr oc- ocb occ ocg oco ocr oeb oec oee oeg oeo oer ogc oge ogg ogo oo- oob ooc oog ooo oor or- orb orc ore org oro orr rbb rbc rbe rbg rbo rbr rcb rcc rce rcg rco rcr re- reb rec ree reg reo rer rgb rgc rge rgg rgo rgr rob roc roe rog roo ror rrb rrc rrg rrr