function trackback(num){
	switch (num){
		case 1:
			document.getElementById('show_tb').style.display = 'block';
			document.getElementById('hide_tb').style.display = 'none';
			break;
		case 0:
			document.getElementById('show_tb').style.display = 'none';
			document.getElementById('hide_tb').style.display = 'block';
			break;

	}

}