\BOOKMARK [1][-]{section.1}{Introduction}{}% 1
\BOOKMARK [1][-]{section.2}{Auxiliary results for the first identity of Theorem 1}{}% 2
\BOOKMARK [1][-]{section.3}{Auxiliary results for the second identity of Theorem 1}{}% 3
\BOOKMARK [1][-]{section.4}{Proof of the main result}{}% 4
\BOOKMARK [1][-]{section.5}{Final remarks}{}% 5
\BOOKMARK [1][-]{section.6}{Acknowledgments}{}% 6