// JavaScript Document
var subBook;

function init() {
    subBook = document.getElementById('sub-book');
    subBook.style.visibility = "hidden";
	
}
function hideSubBook(){
    if (subBook.style.visibility != "hidden") {
        subBook.style.visibility = "hidden";
    }
}
function showSubBook(){
    if (subBook.style.visibility != "visible") {
        subBook.style.visibility = "visible";
    }
}