If we multiply both sides by d/2, and since d/2=−d/2(modd), we obtain d2(∑i=12k+1fE(ei)+∑i=12s+1fE(ei′))=0(modd). Using the odd cycle property of (C,fE), we obtain d2∑i=12s+1fE(ei′)=0(modd), which means that (2.1) holds for C′ too. □ The following ...