diff --git a/tests/playground/rbmap4.lean b/tests/playground/rbmap4.lean
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+/-
+Copyright (c) 2017 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura
+-/
+prelude
+import init.data.ordering.basic init.coe init.data.option.basic init.io
+
+universes u v w w'
+
+inductive color
+| Red | Black
+
+inductive Tree
+| Leaf  {}                                                                       : Tree
+| Node  (color : color) (lchild : Tree) (key : Nat) (val : Bool) (rchild : Tree) : Tree
+
+variables {σ : Type w}
+open color Nat Tree
+
+def fold (f : Nat → Bool → σ → σ) : Tree → σ → σ
+| Leaf b               := b
+| (Node _ l k v r)   b := fold r (f k v (fold l b))
+
+@[inline]
+def balance1 : Nat → Bool → Tree → Tree → Tree
+| kv vv t (Node _ (Node Red l kx vx r₁) ky vy r₂) := Node Red (Node Black l kx vx r₁) ky vy (Node Black r₂ kv vv t)
+| kv vv t (Node _ l₁ ky vy (Node Red l₂ kx vx r)) := Node Red (Node Black l₁ ky vy l₂) kx vx (Node Black r kv vv t)
+| kv vv t (Node _ l  ky vy r)                     := Node Black (Node Red l ky vy r) kv vv t
+| _  _  _                                       _ := Leaf
+
+@[inline]
+def balance2 : Tree → Nat → Bool → Tree → Tree
+| t kv vv (Node _ (Node Red l kx₁ vx₁ r₁) ky vy r₂)  := Node Red (Node Black t kv vv l) kx₁ vx₁ (Node Black r₁ ky vy r₂)
+| t kv vv (Node _ l₁ ky vy (Node Red l₂ kx₂ vx₂ r₂)) := Node Red (Node Black t kv vv l₁) ky vy (Node Black l₂ kx₂ vx₂ r₂)
+| t kv vv (Node _ l ky vy r)                         := Node Black t kv vv (Node Red l ky vy r)
+| _ _ _                                         _    := Leaf
+
+def isRed : Tree → Bool
+| (Node Red _ _ _ _) := true
+| _                  := false
+
+def ins : Tree → Nat → Bool → Tree
+| Leaf                 kx vx := Node Red Leaf kx vx Leaf
+| (Node Red a ky vy b) kx vx :=
+   (if kx < ky then Node Red (ins a kx vx) ky vy b
+    else if kx = ky then Node Red a kx vx b
+    else Node Red a ky vy (ins b kx vx))
+| (Node Black a ky vy b) kx vx :=
+    if kx < ky then
+      (if isRed a then balance1 ky vy b (ins a kx vx)
+       else Node Black (ins a kx vx) ky vy b)
+    else if kx = ky then Node Black a kx vx b
+    else if isRed b then balance2 a ky vy (ins b kx vx)
+         else Node Black a ky vy (ins b kx vx)
+
+def setBlack : Tree → Tree
+| (Node _ l k v r) := Node Black l k v r
+| e                := e
+
+def insert (t : Tree) (k : Nat) (v : Bool) : Tree :=
+if isRed t then setBlack (ins t k v)
+else ins t k v
+
+def mkMapAux : Nat → Tree → Tree
+| 0 m := m
+| (n+1) m := mkMapAux n (insert m n (n % 10 = 0))
+
+def mkMap (n : Nat) :=
+mkMapAux n Leaf
+
+def main (xs : List String) : IO UInt32 :=
+let m := mkMap xs.head.toNat in
+let v := fold (λ (k : Nat) (v : Bool) (r : Nat), if v then r + 1 else r) m 0 in
+IO.println (toString v) *>
+pure 0