function toggleLevel(id) {
    var level = document.getElementById('c'+id);
    var img = document.getElementById('i'+id);
    if(level.style.display == 'block') {
        hideLevel(level, img);
    } else {
	showLevel(level, img);
    }
}

function hideLevel(id) {
    var level = document.getElementById('c'+id);
    var img = document.getElementById('i'+id);
    hideLevel(level, img);
}

function hideLevel(level, img) {
    level.style.display = "none";
    img.src = '/img/plus.gif';
}

function showLevel(id) {
    var level = document.getElementById('c'+id);
    var img = document.getElementById('i'+id);
    showLevel(level, img);
}

function showLevel(level, img) {
    level.style.display = 'block';
    img.src = '/img/minus.gif';
}