diff --git a/src_colibri2/core/colibri2_core.mli b/src_colibri2/core/colibri2_core.mli
index 0b2d84901c2cff5f8e06753c807048760dc23528..fa2dae87b9a9ca718374c53430487c80f2175c64 100644
--- a/src_colibri2/core/colibri2_core.mli
+++ b/src_colibri2/core/colibri2_core.mli
@@ -53,22 +53,25 @@ module rec Egraph : sig
   (** Egraph where its structure can not be modified *)
 
   val is_equal : _ t -> Node.t -> Node.t -> bool
+  (** Tests if two nodes are equal *)
 
   val find_def : _ t -> Node.t -> Node.t
+  (** [find_def d n] finds the representative of the equivalence class of [n] *)
+
+  val find : _ t -> Node.t -> Node.t
+
+  val is_repr : _ t -> Node.t -> bool
 
   val get_dom : _ t -> 'a Dom.Kind.t -> Node.t -> 'a option
-  (** dom of the class *)
+  (** [get_dom d dom n] returns the domain [dom] of the node [n] if it is set *)
 
   val get_value : _ t -> Node.t -> Value.t option
-  (** one of the value of the class *)
+  (** [get_value d n] returns the value of the node [n] if set *)
 
   (** {4 The classes must have been registered} *)
 
-  val find : _ t -> Node.t -> Node.t
-
-  val is_repr : _ t -> Node.t -> bool
-
   val is_registered : _ t -> Node.t -> bool
+  (** [is_registered n] tests if [n] is registered *)
 
   val get_env : _ t -> 'a Env.Saved.t -> 'a
   (** Can raise UninitializedEnv *)
@@ -79,8 +82,6 @@ module rec Egraph : sig
 
   val context : _ t -> Context.creator
 
-  val contradiction : _ t -> 'a
-
   val register : _ t -> Node.t -> unit
   (** Add a new node to register *)
 
@@ -99,8 +100,14 @@ module rec Egraph : sig
   (** attach value to an equivalence class *)
 
   val merge : rw t -> Node.t -> Node.t -> unit
+  (** [merge n1 n2] Asks to merge the equivalence class of [n1] and [n2] *)
+
+  val contradiction : _ t -> 'a
+  (** raises {!Contradiction} *)
 
   exception Contradiction
+
+  exception NotRegistered
 end
 
 (** {3 Ground terms} *)