function submenu(){
	document.getElementById("menu_invent").onmouseover = function(){document.getElementById("submenu_invent").style.display = "block"};
	document.getElementById("menu_invent").onmouseout = function(){document.getElementById("submenu_invent").style.display = "none"};

	document.getElementById("menu_corres").onmouseover = function(){document.getElementById("submenu_corres").style.display = "block"};
	document.getElementById("menu_corres").onmouseout = function(){document.getElementById("submenu_corres").style.display = "none"};	
}