function fold_category(id) {
	var target = document.getElementById(id).style;
	if(target.display == "none") {
		target.display = "block";
	} else {
		target.display = "none";
	}
	return false;
}

function swap_image(id, img1, img2) {
	var target = document.getElementById(id);
	if(target.src == img1) {
		target.src = img2;
	} else if(target.src == img2) {
		target.src = img1;
	}
	return ;
}