diff --git a/lib/term.ml b/lib/term.ml
index 128590f..7e49062 100644
--- a/lib/term.ml
+++ b/lib/term.ml
@@ -20,6 +20,7 @@ type t =
   | App of t * t
 [@@deriving eq, ord, show]
 
+(** string of Term *)
 let rec string_of_term = function
   | Var v -> "Var '" ^ v ^ "'"
   | IntConst n -> string_of_int n
diff --git a/lib/type.ml b/lib/type.ml
index acac45e..06a6af0 100644
--- a/lib/type.ml
+++ b/lib/type.ml
@@ -5,6 +5,7 @@ type t =
   | Arrow of t * t
 [@@deriving eq, ord, show]
 
+(** string of Type *)
 let rec string_of_type = function
   | Var v -> "Var '" ^ v ^ "'"
   | Int -> "Int"
diff --git a/lib/typeSubstitution.ml b/lib/typeSubstitution.ml
index c6a5e41..cd12f65 100644
--- a/lib/typeSubstitution.ml
+++ b/lib/typeSubstitution.ml
@@ -39,6 +39,7 @@ let compose s2 s1 =
     s2
 ;;
 
+(** string of IdentifierMap *)
 let to_string map =
   let rec ty_str = function
     | Type.Var s -> "Var('" ^ s ^ "')"
@@ -53,8 +54,10 @@ let to_string map =
   ^ "}"
 ;;
 
+(** Find an element in an IdentifierMap *)
 let find = IdentifierMap.find_opt
 
+(** Check if two IdentifierMap are equal *)
 let equal map1 map2 =
   let l_map1 = List.length (IdentifierMap.bindings map1) in
   let l_map2 = List.length (IdentifierMap.bindings map2) in