function over(img){
	document.getElementById(img).src = "./img/"+img+"_over.png";
}
function out(img){
	document.getElementById(img).src = "./img/"+img+".png";
}

function aparece(div){
	document.getElementById(div).style.visibility = "visible";
}
function desaparece(div){
	document.getElementById(div).style.visibility = "hidden";
}