var gnCurrentPage = 0;

  function getPage(nPage) {
    return document.getElementById("tippage" + nPage)
  }  

  function enableNavLinks() {
    if (getPage(gnCurrentPage-1) == null) {
      document.getElementById("aPrev").disabled = true;
      document.getElementById("aPrev").style.color = "gray";
    }
    else {
      document.getElementById("aPrev").disabled = false;
      document.getElementById("aPrev").style.color = "";
    }
    
    if (getPage(gnCurrentPage+1) == null) {
      document.getElementById("aNext").disabled = true;
      document.getElementById("aNext").style.color = "gray";
    }
    else {
      document.getElementById("aNext").disabled = false;
      document.getElementById("aNext").style.color = "";
    }
  }
    
  function nextPage() {
    gnCurrentPage++;

    if (!openPage())
      gnCurrentPage--;
    
    return false;
  }

  function openPage() {
    if (!getPage(gnCurrentPage)) return false;
    
    document.getElementById("divCurrentPage").innerHTML =
      getPage(gnCurrentPage).innerHTML;
    
    enableNavLinks();      
    
    return true;
  }
  
  function previousPage() {
    gnCurrentPage--;
    
    if (!openPage())
      gnCurrentPage++;
    
    return false;
  }
  
  function initTipPage() {
    nextPage();
  }
  
  window.onload = initTipPage;