diff --git a/theories/map.why b/theories/map.why
index d6e07a74350613f5f6b3fa597375ee439aa34c14..e47d4755e96576115738d4b5ad2f40a340a18f35 100644
--- a/theories/map.why
+++ b/theories/map.why
@@ -95,6 +95,7 @@ end
 
 (** {2 Number of occurrences} *)
 
+(* TODO: we could define Occ using theory int.NumOf *)
 theory Occ
 
   use import int.Int