diff --git a/trees-that-shrink/TreesThatShrink.ipynb b/trees-that-shrink/TreesThatShrink.ipynb
index 882fbde..0c198c9 100644
--- a/trees-that-shrink/TreesThatShrink.ipynb
+++ b/trees-that-shrink/TreesThatShrink.ipynb
@@ -143,7 +143,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -170,7 +170,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -189,7 +189,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -224,7 +224,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 8,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -259,7 +259,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 9,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -297,7 +297,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 10,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -322,7 +322,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -343,7 +343,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 12,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -354,7 +354,7 @@
     "    AbsUD f -> eval env f\n",
     "    AppUD f x -> let\n",
     "        x' = eval env x\n",
-    "        in eval (x':env) f"
+    "        in eval (env ++ [x']) f"
    ]
   },
   {
@@ -366,13 +366,13 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 13,
+   "execution_count": null,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "2"
+       "1"
       ]
      },
      "metadata": {},
@@ -381,7 +381,7 @@
    ],
    "source": [
     "identity = AbsLet \"i\" (VarLet \"i\")\n",
-    "konst = (AbsLet \"x\" (AbsLet \"y\" (VarLet \"x\")))\n",
+    "konst = AbsLet \"x\" (AbsLet \"y\" (VarLet \"x\"))\n",
     "\n",
     "eval [] . anonymise . desugar Map.empty $ AppLet (AppLet konst (LitLet 1)) (LitLet 2)"
    ]
@@ -402,7 +402,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 14,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -496,11 +496,12 @@
   "language_info": {
    "codemirror_mode": "ihaskell",
    "file_extension": ".hs",
+   "mimetype": "text/x-haskell",
    "name": "haskell",
    "pygments_lexer": "Haskell",
-   "version": "8.2.2"
+   "version": "9.4.8"
   }
  },
  "nbformat": 4,
- "nbformat_minor": 2
+ "nbformat_minor": 4
 }
diff --git a/trees-that-shrink/default.nix b/trees-that-shrink/default.nix
index be3ac50..74b7e31 100644
--- a/trees-that-shrink/default.nix
+++ b/trees-that-shrink/default.nix
@@ -1,7 +1,20 @@
 let
   pkgs = import ../pkgs.nix;
-in import "${pkgs.ihaskell}/release.nix" {
-  compiler = "ghc928";
-  nixpkgs = import pkgs.nixpkgs {};
+  overlay = sel: sup: {
+    nix-filter = import pkgs.nix-filter;
+    haskell = sup.haskell // {
+      packages = sup.haskell.packages // {
+        ghc948 = sup.haskell.packages.ghc948.override {
+          overrides = self: super: {
+            ghc-syntax-highlighter = self.ghc-syntax-highlighter_0_0_10_0;
+          };
+        };
+      };
+    };
+  };
+  nixpkgs = (import pkgs.nixpkgs { overlays = [ overlay ]; });
+  jupyterlab = nixpkgs.python3.withPackages (ps: [ ps.jupyterlab ps.notebook ]);
+in nixpkgs.callPackage "${pkgs.ihaskell}/nix/release.nix" { compiler = "ghc948"; }{
   packages = self: with self; [ containers ];
+  extraEnvironmentBinaries = [jupyterlab];
 }