diff --git a/lib/ir/nier_simple.mli b/lib/ir/nier_simple.mli
index f8ed9f1b616a99f2e2853710a4946c72b03d5b90..1824367fc08517c6c75f0f77ae80c8365ff50ded 100644
--- a/lib/ir/nier_simple.mli
+++ b/lib/ir/nier_simple.mli
@@ -11,6 +11,7 @@ module Shape : sig
   val set : t -> int -> int -> t
   val row_major : t -> int array -> int
   val unrow_major : t -> int -> int array
+
 end
 
 module Tensor : sig
@@ -129,7 +130,7 @@ type descr =
   | Log of { input : node }
 
 and node = private {
-  id : int;
+  id : int; (* unique identifier *)
   descr : descr;
   shape : Shape.t;
   ty : ty;
@@ -185,7 +186,8 @@ val pp : t Fmt.t
 val pp_debug : t Fmt.t
 
 val create : node -> t
-(** Create a network from its output node *)
+(** Create a network from its output node,
+    it must have only one input *)
 
 val output : t -> node
 (** Output node of the network *)