var plusImg = new Image();
	plusImg.src = "../imagenes/bt_mas.gif"
var minusImg = new Image();
	minusImg.src = "../imagenes/bt_menos.gif"

function hideLevel( _levelId, _imgId ) {
	var thisLevel = document.getElementById( _levelId );
	var thisImg = document.getElementById( _imgId );
	thisLevel.style.display = "none";
	thisImg.src = plusImg.src;
	}
	
function showLevel( _levelId, _imgId ) {
	
	var thisLevel = document.getElementById( _levelId );
	var thisImg = document.getElementById( _imgId );
	if ( thisLevel.style.display == "none") {
		thisLevel.style.display = "block";
		thisImg.src = minusImg.src;
		}
	else {
		hideLevel( _levelId, _imgId);
		}
		
	}