var uplayer = null;

function hide(layername) {
	if (layername && document.getElementById && document.getElementById(layername)) {
		_hide(document.getElementById(layername));
	    if (uplayer == layername) {
	        uplayer = null;
	    }
		return false;
	}
	return true;
}

function show(layername, hidelast) {
	if (layername && document.getElementById && document.getElementById(layername)) {
	    if (uplayer && hidelast) {
	        hide(uplayer);
	    }
		_show(document.getElementById(layername));
		uplayer = layername;
		return false;
	}
	return true;
}

function _hide(layerobject) {
	layerobject.style.display = 'none';
}
function _show(layerobject) {
	layerobject.style.display = 'block';
}