x(fνg^νgνf^ν)dx=x22(f^ν(fν+1+gν+1)g^ν(fν+1gν+1)fν(f^ν+1+g^ν+1)+gν(f^ν+1g^ν+1))=12x(fνf^νfνf^ν+gνg^νgνg^ν),