var color = 0;
var suma = 10;
function aparecer(){
var obj = document.getElementById('content');
obj.style.display = "block";
color += suma;
if (!(color>=110)){
obj.style.filter = 'alpha(opacity='+color+')';
			 obj.style.opacity = color /100;
			 obj.style.MozOpacity = color /100;
			 obj.style.KHTMLOpacity = color /100;
		window.setTimeout ("aparecer();", 100);
}
}
function desvanecer() {
var obj2 = document.getElementById('content');
		color -= suma;
	if (!(color <=-10)){
	obj2.style.filter = 'alpha(opacity='+color+')';
			 obj2.style.opacity = color /100;
			 obj2.style.MozOpacity = color /100;
			 obj2.style.KHTMLOpacity = color /100;
		window.setTimeout ("desvanecer();", 100);
	}
	}
	
function llama(){
if (color<=0){
  aparecer();
}

/*else {
  desvanecer();
}*/
}