function m_swap_n(obj) {
	var el = obj.firstChild.firstChild;
	if (el.className == 'vis png' ) {
		el.className = 'nvis png'; el.nextSibling.className = 'vis png';
	} else {
		el.className = 'vis png'; el.nextSibling.className = 'nvis png';
	}
}