function show(id)
{

   eval("document.getElementById('" + id + "').style.display = ( document.getElementById('" + id + "').style.display == 'block' ? 'none' : 'block');");

}	

function show_practice()
{
	document.getElementById('practices').style.display = 'block';
	document.getElementById('theories').style.display = 'none';
	document.getElementById('link_practice').className = 'active';
	document.getElementById('link_theory').className = '';
}
function show_theory()
{
	document.getElementById('theories').style.display = 'block';
	document.getElementById('practices').style.display = 'none';
	document.getElementById('link_theory').className = 'active';
	document.getElementById('link_practice').className = '';
}