diff --git a/src/core/CCBool.ml b/src/core/CCBool.ml
index 89a6a9e5..6478f5ee 100644
--- a/src/core/CCBool.ml
+++ b/src/core/CCBool.ml
@@ -7,6 +7,8 @@ let equal (a:bool) b = Pervasives.(=) a b
 
 let compare (a:bool) b = Pervasives.compare a b
 
+let leq (a:bool) b = Pervasives.(<=) a b
+
 let negate = not
 
 type 'a printer = Format.formatter -> 'a -> unit
diff --git a/src/core/CCBool.mli b/src/core/CCBool.mli
index 3ba02bb2..002f7f1e 100644
--- a/src/core/CCBool.mli
+++ b/src/core/CCBool.mli
@@ -8,6 +8,10 @@ type t = bool
 val compare : t -> t -> int
 (** Total ordering on booleans, similar to {!Pervasives.compare}. *)
 
+val leq : t -> t -> bool
+(** Equivalent of [(<=)]
+    Allows to be passed to {!Heap.Make} *)
+
 val equal : t -> t -> bool
 
 val negate : t -> t
diff --git a/src/core/CCChar.ml b/src/core/CCChar.ml
index 42036003..7e03c870 100644
--- a/src/core/CCChar.ml
+++ b/src/core/CCChar.ml
@@ -8,6 +8,8 @@ include Char
 
 let equal (a:char) b = Pervasives.(=) a b
 
+let leq (a:char) b = Pervasives.(<=) a b
+
 let pp_buf = Buffer.add_char
 let pp = Format.pp_print_char
 
diff --git a/src/core/CCChar.mli b/src/core/CCChar.mli
index 974e9096..c735188b 100644
--- a/src/core/CCChar.mli
+++ b/src/core/CCChar.mli
@@ -15,6 +15,10 @@ val compare : t -> t -> int
     allows the module [Char] to be passed as argument to the functors
     {!Set.Make} and {!Map.Make}. *)
 
+val leq : t -> t -> bool
+(** Equivalent of [(<=)]
+    Allows to be passed to {!Heap.Make} *)
+
 val lowercase_ascii : t -> t
 (** Convert the given character to its equivalent lowercase character,
     using the US-ASCII character set.
diff --git a/src/core/CCFloat.ml b/src/core/CCFloat.ml
index 6edd5feb..fc70b703 100644
--- a/src/core/CCFloat.ml
+++ b/src/core/CCFloat.ml
@@ -76,6 +76,7 @@ let equal (a:float) b = a=b
 
 let hash : t -> int = Hashtbl.hash
 let compare (a:float) b = Pervasives.compare a b
+let leq (a:float) b = Pervasives.(<=) a b
 
 type 'a printer = Format.formatter -> 'a -> unit
 type 'a random_gen = Random.State.t -> 'a
diff --git a/src/core/CCFloat.mli b/src/core/CCFloat.mli
index a4778766..fdad62f9 100644
--- a/src/core/CCFloat.mli
+++ b/src/core/CCFloat.mli
@@ -55,6 +55,10 @@ val equal : t -> t -> bool
 
 val compare : t -> t -> int
 
+val leq : t -> t -> bool
+(** Equivalent of [(<=)]
+    Allows to be passed to {!Heap.Make} *)
+
 type 'a printer = Format.formatter -> 'a -> unit
 type 'a random_gen = Random.State.t -> 'a
 
diff --git a/src/core/CCInt.ml b/src/core/CCInt.ml
index f260c719..56bc6e20 100644
--- a/src/core/CCInt.ml
+++ b/src/core/CCInt.ml
@@ -7,6 +7,8 @@ let equal (a:int) b = Pervasives.(=) a b
 
 let compare a b = compare a b
 
+let leq (a:int) b = Pervasives.(<=) a b
+
 let hash i = i land max_int
 
 let range i j yield =
diff --git a/src/core/CCInt.mli b/src/core/CCInt.mli
index 48ef8ac4..86725ded 100644
--- a/src/core/CCInt.mli
+++ b/src/core/CCInt.mli
@@ -11,6 +11,10 @@ val compare : t -> t -> int
 val equal : t -> t -> bool
 (** Equality function for integers. *)
 
+val leq : t -> t -> bool
+(** Equivalent of [(<=)]
+    Allows to be passed to {!Heap.Make} *)
+
 val hash : t -> int
 
 val sign : t -> int
diff --git a/src/core/CCInt32.ml b/src/core/CCInt32.ml
index 74aaab63..6dc27a1b 100644
--- a/src/core/CCInt32.ml
+++ b/src/core/CCInt32.ml
@@ -2,7 +2,8 @@
 
 include Int32
 
-let equal (x:t) y = Pervasives.(=) x y
+let equal (x:int32) y = Pervasives.(=) x y
+let leq (a:int32) b = Pervasives.(<=) a b
 
 module Infix = struct
   let (+) = add
diff --git a/src/core/CCInt32.mli b/src/core/CCInt32.mli
index 33a0cfab..dc687dd0 100644
--- a/src/core/CCInt32.mli
+++ b/src/core/CCInt32.mli
@@ -94,6 +94,10 @@ val equal : t -> t -> bool
 (** The equal function for 32-bit integers.
     Like {!Pervasives.(=) x y)}. *)
 
+val leq : t -> t -> bool
+(** Equivalent of [(<=)]
+    Allows to be passed to {!Heap.Make} *)
+
 val hash : t -> int
 (** Like {!Pervasives.abs (to_int x)}. *)
 
diff --git a/src/core/CCInt64.ml b/src/core/CCInt64.ml
index bfaed6f9..ec1470e9 100644
--- a/src/core/CCInt64.ml
+++ b/src/core/CCInt64.ml
@@ -2,7 +2,8 @@
 
 include Int64
 
-let equal (x:t) y = Pervasives.(=) x y
+let equal (x:int64) y = Pervasives.(=) x y
+let leq (a:int64) b = Pervasives.(<=) a b
 
 module Infix = struct
   let (+) = add
diff --git a/src/core/CCInt64.mli b/src/core/CCInt64.mli
index 6d6b7214..cee073d2 100644
--- a/src/core/CCInt64.mli
+++ b/src/core/CCInt64.mli
@@ -100,6 +100,10 @@ val compare : t -> t -> int
     allows the module [CCInt64] to be passed as argument to the functors
     {!Set.Make} and {!Map.Make}. *)
 
+val leq : t -> t -> bool
+(** Equivalent of [(<=)]
+    Allows to be passed to {!Heap.Make} *)
+
 val hash : t -> int
 (** Like {!Pervasives.abs (to_int x)}. *)
 
diff --git a/src/core/CCString.ml b/src/core/CCString.ml
index c127e097..b11c9bbb 100644
--- a/src/core/CCString.ml
+++ b/src/core/CCString.ml
@@ -66,6 +66,8 @@ let equal (a:string) b = Pervasives.(=) a b
 let compare_int (a : int) b = Pervasives.compare a b
 let compare = String.compare
 
+let leq (a:string) b = String.compare a b <= 0
+
 let hash s = Hashtbl.hash s
 
 let length = String.length
diff --git a/src/core/CCString.mli b/src/core/CCString.mli
index eb4734f2..af821595 100644
--- a/src/core/CCString.mli
+++ b/src/core/CCString.mli
@@ -64,6 +64,10 @@ val equal : string -> string -> bool
 
 val compare : string -> string -> int
 
+val leq : t -> t -> bool
+(** Equivalent of [(<=)]
+    Allows to be passed to {!Heap.Make} *)
+
 val is_empty : string -> bool
 (** [is_empty s] returns [true] iff [s] is empty (i.e. its length is 0).
     @since 1.5 *)
diff --git a/src/core/CCUtf8_string.ml b/src/core/CCUtf8_string.ml
index 60ccf1b5..ad6e6044 100644
--- a/src/core/CCUtf8_string.ml
+++ b/src/core/CCUtf8_string.ml
@@ -10,6 +10,7 @@ type 'a gen = unit -> 'a option
 type 'a sequence = ('a -> unit) -> unit
 
 let equal (a:string) b = Pervasives.(=) a b
+let leq (a:string) b = String.compare a b <= 0
 let hash : string -> int = Hashtbl.hash
 let pp = Format.pp_print_string
 
diff --git a/src/core/CCUtf8_string.mli b/src/core/CCUtf8_string.mli
index 8bec9722..b88bbcf6 100644
--- a/src/core/CCUtf8_string.mli
+++ b/src/core/CCUtf8_string.mli
@@ -29,6 +29,10 @@ val hash : t -> int
 
 val compare : t -> t -> int
 
+val leq : t -> t -> bool
+(** Equivalent of [(<=)]
+    Allows to be passed to {!Heap.Make} *)
+
 val pp : Format.formatter -> t -> unit
 
 val to_string : t -> string