\BOOKMARK [1][-]{section.1}{Introduction}{}% 1
\BOOKMARK [1][-]{section.2}{Lower and upper bounds for }{}% 2
\BOOKMARK [1][-]{section.3}{Upper bound for }{}% 3
\BOOKMARK [1][-]{section.4}{\(Not so sharp\) lower bound for }{}% 4
\BOOKMARK [1][-]{section.5}{Conjectures}{}% 5
\BOOKMARK [1][-]{section.6}{Acknowledgements}{}% 6