function destruction(myId) {
    var parent = document.getElementById(myId).parentNode;
    parent.removeChild(document.getElementById(myId));
  }  
  
  function move_porte_gauche() {
    new Effect.Parallel([
	  new Effect.Move("porte_gauche", { sync: true, x: -650, y: 0, mode: 'relative' }),
	  new Effect.Opacity("porte_gauche", { sync: true, from: 1, to: 0 })
	], {
	  duration: 4, 
	  delay: 0.2 
	});  
	setTimeout("destruction(\"porte_gauche\")", 4000);
  }
  
  function move_porte_droite() {
    new Effect.Parallel([
	  new Effect.Move("porte_droite", { sync: true, x: 571, y: 0, mode: 'relative' }),
	  new Effect.Opacity("porte_droite", { sync: true, from: 1, to: 0 })
	], { 
	  duration: 4, 
	  delay: 0.2 
	});
	setTimeout("destruction(\"porte_droite\")", 4000);
  }