var intros = [];
var initialized = false;
function init() {
	intros[0] = document.getElementById('intro');
	intros[1] = document.getElementById('intro_1');
	intros[2] = document.getElementById('intro_2');
	intros[3] = document.getElementById('intro_3');		
	initialized = true;
};
function showover(id) {
	if (! initialized) init();
	for (i=0; i<4; i++) {
		if (i != id) {
			intros[i].style.display = 'none';
		};
	};
	intros[id].style.display = 'block';
};