function on(id)
	{
		ddmenuitem = document.getElementById(id);
		ddmenuitem.style.visibility = 'visible';
	
	}
	
	function off(id)
	{
		ddmenuitem = document.getElementById(id);
		ddmenuitem.style.visibility = 'hidden';
	}
	
	function contact_validate(form)
	{
		with(form)
		{
			if(validate_required(name,"Please enter your name!")==false)
			{
				name.focus();
				return false;
			}
			if(validate_required(email, "Please enter your E-Mail address!")==false)
			{
				email.focus();
				return false;
			}
			
			if(email_validation(email.value)==false)
			{
				email.focus();
	document.getElementById('error_body').firstChild.nodeValue="Please enter a valid E-Mail address!";
	    	on('error');
	    	return false;
			}
			
			return true;
		}	
	}
	
	function email_validation(email)
	{
		var valid_email = new RegExp(".+@.+\\.[a-z]{2,3}");
		
		if(valid_email.test(email))
		{
			return true;	
		}
		else
		{
			return false;
		}
	}
	
	function validate_required(field,alerttxt)
	{
	with (field)
	  {
	  if (value==null||value=="")
	    {
	    	document.getElementById('error_body').firstChild.nodeValue=alerttxt;
	    	on('error');
	    	return false;
	    }
	  else
	    {
	    return true;
	    }
	  }
	}
	
	function sum(changed){

		var a = document.getElementById('a').value;
		var b = document.getElementById('b').value;
		var c = document.getElementById('c').value;
		var d = document.getElementById('d').value;
		var e = document.getElementById('e').value;
		var f = document.getElementById('f').value;
		var g = document.getElementById('g').value;
		var h = document.getElementById('h').value;
		var i = document.getElementById('i').value;
		
		
		
			var change = document.getElementById(changed).value;
			var unique = true;
			
			if(changed == 'a' && change != "0"){
				if(b==change||c==change||d==change||e==change||f==change||g==change||h==change||i==change||isNaN(a)||a>9||change==""||change==" "){
					unique = false;
					var oldNum = Number(document.getElementById('2').value) - Number(document.getElementById('c').value) - Number(document.getElementById('b').value);
					document.getElementById('a').value = oldNum;
					
				}
			}
			else if(changed == 'b' && change != "0"){
				if(a==change||c==change||d==change||e==change||f==change||g==change||h==change||i==change||isNaN(b)||b>9||change==""||change==" "){
					unique = false;
					var oldNum = Number(document.getElementById('2').value) - Number(document.getElementById('c').value) - Number(document.getElementById('a').value);
					document.getElementById('b').value = oldNum;
				}
			}
			else if(changed == 'c' && change != "0"){
				if(b==change||a==change||d==change||e==change||f==change||g==change||h==change||i==change||isNaN(c)||c>9||change==""||change==" "){
					unique = false;
					var oldNum = Number(document.getElementById('2').value) - Number(document.getElementById('a').value) - Number(document.getElementById('b').value);
					document.getElementById('c').value = oldNum;
				}
			}
			else if(changed == 'd' && change != "0"){
				if(b==change||c==change||a==change||e==change||f==change||g==change||h==change||i==change||isNaN(d)||d>9||change==""||change==" "){
					unique = false;
					var oldNum = Number(document.getElementById('3').value) - Number(document.getElementById('e').value) - Number(document.getElementById('f').value);
					document.getElementById('d').value = oldNum;
				}
			}
			else if(changed == 'e' && change != "0"){
				if(b==change||c==change||d==change||a==change||f==change||g==change||h==change||i==change||isNaN(e)||e>9||change==""||change==" "){
					unique = false;
					var oldNum = Number(document.getElementById('3').value) - Number(document.getElementById('f').value) - Number(document.getElementById('d').value);
					document.getElementById('e').value = oldNum;
				}
			}
			else if(changed == 'f' && change != "0"){
				if(b==change||c==change||d==change||e==change||a==change||g==change||h==change||i==change||isNaN(f)||f>9||change==""||change==" "){
					unique = false;
					var oldNum = Number(document.getElementById('3').value) - Number(document.getElementById('d').value) - Number(document.getElementById('e').value);
					document.getElementById('f').value = oldNum;
				}
			}
			else if(changed == 'g' && change != "0"){
				if(b==change||c==change||d==change||e==change||f==change||a==change||h==change||i==change||isNaN(g)||g>9||change==""||change==" "){
					unique = false;
					var oldNum = Number(document.getElementById('4').value) - Number(document.getElementById('h').value) - Number(document.getElementById('i').value);
					document.getElementById('g').value = oldNum;
				}
			}
			else if(changed == 'h' && change != "0"){
				if(b==change||c==change||d==change||e==change||f==change||g==change||a==change||i==change||isNaN(h)||h>9||change==""||change==" "){
					unique = false;
					var oldNum = Number(document.getElementById('4').value) - Number(document.getElementById('g').value) - Number(document.getElementById('i').value);
					document.getElementById('h').value = oldNum;
				}
			}
			else if(changed == 'i' && change != "0"){
				if(b==change||c==change||d==change||e==change||f==change||g==change||h==change||a==change||isNaN(i)||i>9||change==""||change==" "){
					unique = false;
					var oldNum = Number(document.getElementById('4').value) - Number(document.getElementById('g').value) - Number(document.getElementById('h').value);
					document.getElementById('i').value = oldNum;
				}
			}
			
			
			
			if(unique){
		
				var sum1 = Number(g)+Number(e)+Number(c);
				document.getElementById("1").value = sum1;
				var sum2 = Number(a)+Number(b)+Number(c);
				document.getElementById("2").value = sum2;
				var sum3 = Number(d)+Number(e)+Number(f);
				document.getElementById("3").value = sum3;
				var sum4 = Number(g)+Number(h)+Number(i);
				document.getElementById("4").value = sum4;
				var sum5 = Number(a)+Number(e)+Number(i);
				document.getElementById("5").value = sum5;
				var sum6 = Number(c)+Number(f)+Number(i);
				document.getElementById("6").value = sum6;
				var sum7 = Number(b)+Number(e)+Number(h);
				document.getElementById("7").value = sum7;
				var sum8 = Number(a)+Number(d)+Number(g);
				document.getElementById("8").value = sum8;
				
				if(sum1==15&&sum2==15&&sum3==15&&sum4==15&&sum5==15&&sum6==15&&sum7==15&&sum8==15){
					alert("Congratulations! You have solved the puzzle!");
				}
			}
	
		
		
	
	
	}