var chapters = document.getElementsByName('chapters');

function buy_all() {
	for(i = 0; i < chapters.length; i++) {
		chapters[i].checked = false;
		chapters[i].disabled = true;
	}
}

function buy_some() {
	for(i = 0; i < chapters.length; i++)
		chapters[i].disabled = false;
}

function load() {
	buy_all();
}