diff --git a/sledge/nonstdlib/NS.mli b/sledge/nonstdlib/NS.mli
index 2c2115102..9685eb97a 100644
--- a/sledge/nonstdlib/NS.mli
+++ b/sledge/nonstdlib/NS.mli
@@ -43,7 +43,17 @@ module Poly : sig
   val hash : 'a -> int
 end
 
-module Ord = Containers.Ord
+module Ord : sig
+  include module type of Containers.Ord
+
+  val ( @? ) : 'a t -> 'a t -> 'a t
+
+  module Infix : sig
+    include module type of Containers.Ord.Infix
+
+    val ( @? ) : 'a t -> 'a t -> 'a t
+  end
+end
 
 (** Function combinators *)
 
diff --git a/sledge/nonstdlib/NS0.ml b/sledge/nonstdlib/NS0.ml
index 98f454c4e..cd0331aa1 100644
--- a/sledge/nonstdlib/NS0.ml
+++ b/sledge/nonstdlib/NS0.ml
@@ -55,7 +55,17 @@ module Poly = struct
   let hash = Stdlib.Hashtbl.hash
 end
 
-module Ord = Containers.Ord
+module Ord = struct
+  include Containers.Ord
+
+  let ( @? ) c1 c2 x y = c1 x y <?> (c2, x, y)
+
+  module Infix = struct
+    include Infix
+
+    let ( @? ) = ( @? )
+  end
+end
 
 (** Function combinators *)