var can_hide = true;

function hideSubMenus(len){
  var el;
  for(i = 0; i < len; i++)
    if (el = document.getElementById('submenu'+(i+1)))
	  if (can_hide) el.style.display = 'none';
}

function showSubMenu(num){
  var el;
  if (el = document.getElementById('submenu'+num)) el.style.display = 'block';
  can_hide = false;
}