-er bbb bbc bbe bbo bbr bcb bcc bce bco bcr bcv be- beb bec bee beo ber bev bob boc boe boo bor bov brb bre bro brr brv bvb bvc bve bvo bvr bvv c-- cbb cbc cbe cbo cbr cbv ccb ccc cce cco ccr ccv ce- ceb cec cee ceo cer cev co- cob coc coe coo cor cov crb crc cre cro crr crv cvb cvc cve cvo cvr cvv ebb ebc ebe ebo ebr ebv ec- ecb ecc ece eco ecr ecv eeb eec eee eeo eer eev eo- eob eoc eoe eoo eor erb erc ere ero err erv evb evc eve evo evr evv ob- obb obc obe obo obr obv oc- ocb occ oco ocr ocv oeb oec oee oeo oer oo- oob ooc ooo oor oov or- orb orc ore oro orr orv ov- ovb ovc ove ovo ovv rbb rbc rbe rbo rbr rcb rcc rce rco rcr rcv re- reb rec ree reo rer rev rob roc roe roo ror rov rrb rrc rrr rvb rvc rve rvo rvr rvv v-e vbc vbo vbr vbv vcc vce vco vcr veb vec vee veo ver vob voc voe voo vor vov vrb vrc vre vrr vvb vvc vvo vvr vvv