function show_hide_layer(layer_id, show_or_hide) {
	if (document.getElementById) {
		// this is the way the standards work
		selected_layer = document.getElementById(layer_id);
	}
	else if (document.all) {
		// this is the way old msie versions work
		selected_layer = document.all[layer_id];
	}
	if (show_or_hide == "show" || show_or_hide == "visible") {
		layer_display = "visible";
	}else {
		layer_display = "hidden"
	}
	selected_layer.style.visibility = layer_display;
}

function show_layer(layer_id) {
	
	show_hide_layer(layer_id, "visible");
}

function hide_layer(layer_id) {
	show_hide_layer(layer_id, "hidden");
}