--- stdlib/set.mli.orig	Tue Dec  9 04:11:48 1997
+++ stdlib/set.mli	Thu Jun  4 17:41:07 1998
@@ -50,6 +50,8 @@
     val add: elt -> t -> t
         (* [add x s] returns a set containing all elements of [s],
            plus [x]. If [x] was already in [s], [s] is returned unchanged. *)
+    val make: elt -> t
+        (* [make x] returns a set containing only [x] *)
     val remove: elt -> t -> t
         (* [remove x s] returns a set containing all elements of [s],
            except [x]. If [x] was not in [s], [s] is returned unchanged. *)
--- stdlib/set.ml.orig	Fri Oct 31 07:59:27 1997
+++ stdlib/set.ml	Thu Jun  4 17:41:07 1998
@@ -27,6 +27,7 @@
     val is_empty: t -> bool
     val mem: elt -> t -> bool
     val add: elt -> t -> t
+    val make: elt -> t
     val remove: elt -> t -> t
     val union: t -> t -> t
     val inter: t -> t -> t
@@ -160,6 +161,8 @@
           if c = 0 then t else
           if c < 0 then bal (add x l) v r else bal l v (add x r)
 
+    let make x = Node(Empty, x, Empty, 1)
+
     let rec remove x = function
         Empty -> Empty
       | Node(l, v, r, _) ->
@@ -171,10 +174,16 @@
       match (s1, s2) with
         (Empty, t2) -> t2
       | (t1, Empty) -> t1
-      | (Node(l1, v1, r1, _), t2) ->
-          let (l2, _, r2) = split v1 t2 in
-          join (union l1 l2) v1 (union r1 r2)
-
+      | ((Node(l1, v1, r1, h1) as t1), (Node(l2, v2, r2, h2) as t2)) ->
+          if (h1>=h2) then
+            if (h2=1) then add v2 t1 else
+              let (l2, _, r2) = split v1 t2 in
+              join (union l1 l2) v1 (union r1 r2)
+          else
+            if (h1=1) then add v1 t2 else
+              let (l1, _, r1) = split v2 t1 in
+              join (union l1 l2) v2 (union r1 r2)
+    
     let rec inter s1 s2 =
       match (s1, s2) with
         (Empty, t2) -> Empty