var menu = document.getElementById("menu");
var menutop = document.getElementById("menutop");
var menubottom = document.getElementById("menubottom");
var cov = document.getElementById("cov");
var menuh = 300;
function setmenu(){
if(menu.offsetHeight>menuh){
	if(cov.scrollTop == 0){
	menutop.innerHTML = "";
	}
	if(cov.scrollTop > 0){
	menutop.innerHTML = "<span style='cursor:pointer;' onClick='scrollit(40)'>∧</span>";
	}
	if(menuh + cov.scrollTop < menu.offsetHeight){
	menubottom.innerHTML = "<span style='cursor:pointer;' onClick='scrollit(-40)'>∨</span>";
	}
	if(menuh + cov.scrollTop >= menu.offsetHeight){
	menubottom.innerHTML = "";
	}
}
}

function scrollit(x)
{
cov.scrollTop -= x;
setmenu();
}