function rotate(total,visible,prefix,smer) {
  var next;
  if (total >= visible) {
    if (smer == 'vpred') {
      for (i=1;i<=total;i++) {
        if (document.getElementById(prefix+i).style.display == 'block') {
          if (document.getElementById(prefix+(i+visible)) !== null) {
            document.getElementById(prefix+(i+visible)).style.display = 'block';
            document.getElementById(prefix+i).style.display = 'none';
          }
          break;
        }
      }
    } else {
      for (i=total;i>=1;i--) {
        if (document.getElementById(prefix+i).style.display == 'block') {
          if (document.getElementById(prefix+(i-visible)) !== null) {
            document.getElementById(prefix+(i-visible)).style.display = 'block';
            document.getElementById(prefix+i).style.display = 'none';
          }
          break;
        }
      }
    }
  }
  return false;
}