var blackboard = new Element('img').setProperty('src', 'images/blackboard.png');
function showblackboard() {
	blackboard.setStyles({
		'position': 'absolute',
		'top': '-30px',
		'left': '350px',
		'z-index': 2
	}).addEvent('click', function(){
		this.remove();
		blackboard = new Element('img').setProperty('src', 'images/blackboard.png');
	}).injectInside($('content'));
}