document.getElementById("header_links_div").innerHTML = '<a class="header_link" href="index.html">Home</a> ' +
'<a class="header_link" href="all.html">All</a> ' +
'<a class="header_link" href="mathematical.html">Mathematical Demonstrations</a> ' +
'<a class="header_link" href="games.html">Games</a> ' +
'<a class="header_link" href="apps.html">Android Apps</a> ';