class List( int value; List next; );
	
void printList( List source; ) {
	print( "{ " );
	while ( source != null ) {
		print( source.value );
		source = source.next;
		if ( source != null )
			print( ", " );
		}
	print( " }" );
	}
	
void head( int n; List source; var List dest; ) {
	print( "Enter head( " + n + ", " );
	printList( source );
	print( ", " );
	printList( dest );
	println( " )" );
	if ( n == 0 ) {
		dest = null;
			// At this point
		}
	else {
		dest = new List{ source.value, null }; 
		print( "dest = " );
		printList( dest );
		println( "" );
		head( n - 1, source.next, dest.next );
			// Inside the above invocation
		}
	print( "Exit head( " + n + ", " );
	printList( source );
	print( ", " );
	printList( dest );
	println( " )" );
	}
	
List source, a2, a4, a7, a9, dest;
a9 = new List{ 9, null };
a7 = new List{ 7, a9 };
a4 = new List{ 4, a7 };
a2 = new List{ 2, a4 };
source = a2;
head( 2, source, dest );	// Inside this invocation
printList( source );
println( "" );
printList( dest );
println( "" );