function show_subnav(NAV, isMain) {
	if(isMain == true) {
		var pfeil = document.getElementById("navlink" + NAV);
		var bild1 = "url(images/arrow.jpg)";
		var bild2 = "url(images/arrow2.jpg)";
	} else {
		var pfeil = document.getElementById("subnavlink" + NAV);
		var bild1 = "url(images/arrow_sub.jpg)";
		var bild2 = "url(images/arrow_sub2.jpg)";
	}

	var navigation = document.getElementById("nav" + NAV);
	if(navigation.style.display == "inline") {
		navigation.style.display = "none";
		pfeil.style.backgroundImage = bild1;
	} else {
		pfeil.style.backgroundImage = bild2;
		navigation.style.display = "inline";
	}
}