diff --git a/Algo/Courses/Chapter 6 - Lists (Exercises).md b/Algo/Courses/Chapter 6 - Lists (Exercises).md
index 8fd3335..9f31447 100644
--- a/Algo/Courses/Chapter 6 - Lists (Exercises).md	
+++ b/Algo/Courses/Chapter 6 - Lists (Exercises).md	
@@ -190,12 +190,9 @@ let insert_nth w i list =
 		invalid_arg "negative rank"
 	else
 		let rec insrec i = function
-			[] -> if i > 1 then
-					failwith "out of bound"
-				else
-					x::t
-			| e::E when i = 1 -> x::e::t
-			| e::t -> e::insrec (i - 1) t
+			(1,l) -> x::l
+			| (_, []) -> failwith "out of bound"
+			| (i, e::t) -> e::insrec(i-1, t)
 		in insrec i list;;
 val insert_nth: 'a -> int -> 'a list -> 'a list = <fun>
 	
\ No newline at end of file