class List( int value; List next; );
	
void printList( List source; ) {
	print( "{ " );
	while ( source != null ) {
		print( source.value );
		source = source.next;
		if ( source != null )
			print( ", " );
		}
	println( " }" );
	}
	
void concatList( int level; List source1, source2; var List dest; ) {
	if ( source1 == null ) {
		dest = source2;
			// At this point
		}
	else {
		dest = new List{ source1.value, null }; 
		concatList( level + 1, source1.next, source2, dest.next );
			// Inside the above invocation
		}
	}
	
List source1, source2, a2, a4, a7, a9, dest;
a9 = new List{ 9, null };
a7 = new List{ 7, a9 };
a4 = new List{ 4, null };
a2 = new List{ 2, a4 };
source1 = a7;
source2 = a2;
concatList( 0, source1, source2, dest );	// Inside this invocation
printList( source1 );
printList( source2 );
printList( dest );