diff --git a/docs/data.ipynb b/docs/data.ipynb
index f3afbc0..0b04592 100644
--- a/docs/data.ipynb
+++ b/docs/data.ipynb
@@ -53,7 +53,7 @@
     "project_path = Path(os.getcwd()).parent.resolve() / 'examples/Example'\n",
     "print(f\"$PWD: {project_path}\")\n",
     "server = Server(imports=['Example'], project_path=project_path)\n",
-    "units, invocations = server.tactic_invocations(project_path / \"Example.lean\")"
+    "units = server.tactic_invocations(project_path / \"Example.lean\")"
    ]
   },
   {
@@ -61,7 +61,7 @@
    "id": "c3c1be91-27a5-4481-b09d-a32dbb94b058",
    "metadata": {},
    "source": [
-    "The function returns a tuple `([str], [TacticInvocation])`. The former element is a list of strings containing each compilation unit, comment data included."
+    "The function returns a list of `CompilationUnit` objects, corresponding to each compilation unit in the input Lean file. For performance reasons only the text boundaries are loaded into `CompilationUnit`s."
    ]
   },
   {
@@ -74,13 +74,13 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "==== #0 ====\n",
+      "#0: [14,85]\n",
       "/-- Ensure that Aesop is running -/\n",
       "example : α → α :=\n",
       "  by aesop\n",
       "\n",
       "\n",
-      "==== #1 ====\n",
+      "#1: [85,254]\n",
       "example : ∀ (p q: Prop), p ∨ q → q ∨ p := by\n",
       "  intro p q h\n",
       "  -- Here are some comments\n",
@@ -94,9 +94,12 @@
     }
    ],
    "source": [
-    "for i, u in enumerate(units):\n",
-    "    print(f\"==== #{i} ====\")\n",
-    "    print(u)"
+    "with open(project_path / \"Example.lean\", 'rb') as f:\n",
+    "    content = f.read()\n",
+    "    for i, unit in enumerate(units):\n",
+    "        print(f\"#{i}: [{unit.i_begin},{unit.i_end}]\")\n",
+    "        unit_text = content[unit.i_begin:unit.i_end].decode('utf-8')\n",
+    "        print(unit_text)"
    ]
   },
   {
@@ -104,7 +107,7 @@
    "id": "52e650fc-4a87-445f-8aa8-707ed9e36c03",
    "metadata": {},
    "source": [
-    "The latter is a list of `TacticInvocation`, which contains the `.before` (corresponding to the state before the tactic), `.after` (corresponding to the state after the tactic), and `.tactic` (tactic executed) fields. "
+    "Each `CompilationUnit` includes a list of `TacticInvocation`s, which contains the `.before` (corresponding to the state before the tactic), `.after` (corresponding to the state after the tactic), and `.tactic` (tactic executed) fields. "
    ]
   },
   {
@@ -122,13 +125,33 @@
       "⊢ α → α\n",
       "[Tactic]\n",
       "aesop (using [])\n",
-      "[Afte]\n",
-      "\n",
+      "[After]\n",
+      "\n"
+     ]
+    }
+   ],
+   "source": [
+    "for i in units[0].invocations:\n",
+    "    print(f\"[Before]\\n{i.before}\")\n",
+    "    print(f\"[Tactic]\\n{i.tactic} (using {i.used_constants})\")\n",
+    "    print(f\"[After]\\n{i.after}\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "id": "51f5398b-5416-4dc1-81cd-6d2514758232",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
       "[Before]\n",
       "⊢ ∀ (p q : Prop), p ∨ q → q ∨ p\n",
       "[Tactic]\n",
       "intro p q h (using [])\n",
-      "[Afte]\n",
+      "[After]\n",
       "p q : Prop\n",
       "h : p ∨ q\n",
       "⊢ q ∨ p\n",
@@ -138,7 +161,7 @@
       "⊢ q ∨ p\n",
       "[Tactic]\n",
       "cases h (using ['Eq.refl', 'Or'])\n",
-      "[Afte]\n",
+      "[After]\n",
       "case inl\n",
       "p q : Prop\n",
       "h✝ : p\n",
@@ -151,7 +174,7 @@
       "⊢ q ∨ p\n",
       "[Tactic]\n",
       "apply Or.inr (using ['Or.inr'])\n",
-      "[Afte]\n",
+      "[After]\n",
       "case inl.h\n",
       "p q : Prop\n",
       "h✝ : p\n",
@@ -163,7 +186,7 @@
       "⊢ p\n",
       "[Tactic]\n",
       "assumption (using [])\n",
-      "[Afte]\n",
+      "[After]\n",
       "\n",
       "[Before]\n",
       "case inr\n",
@@ -172,7 +195,7 @@
       "⊢ q ∨ p\n",
       "[Tactic]\n",
       "apply Or.inl (using ['Or.inl'])\n",
-      "[Afte]\n",
+      "[After]\n",
       "case inr.h\n",
       "p q : Prop\n",
       "h✝ : q\n",
@@ -184,25 +207,17 @@
       "⊢ q\n",
       "[Tactic]\n",
       "assumption (using [])\n",
-      "[Afte]\n",
+      "[After]\n",
       "\n"
      ]
     }
    ],
    "source": [
-    "for i in invocations:\n",
+    "for i in units[1].invocations:\n",
     "    print(f\"[Before]\\n{i.before}\")\n",
     "    print(f\"[Tactic]\\n{i.tactic} (using {i.used_constants})\")\n",
-    "    print(f\"[Afte]\\n{i.after}\")"
+    "    print(f\"[After]\\n{i.after}\")"
    ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "id": "51f5398b-5416-4dc1-81cd-6d2514758232",
-   "metadata": {},
-   "outputs": [],
-   "source": []
   }
  ],
  "metadata": {
@@ -221,7 +236,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.12.6"
+   "version": "3.12.7"
   }
  },
  "nbformat": 4,
diff --git a/examples/data.py b/examples/data.py
deleted file mode 100755
index f1d8978..0000000
--- a/examples/data.py
+++ /dev/null
@@ -1,23 +0,0 @@
-#!/usr/bin/env python3
-
-import subprocess
-from pathlib import Path
-from pantograph.server import Server
-
-def get_project_and_lean_path():
-    cwd = Path(__file__).parent.resolve() / 'Example'
-    p = subprocess.check_output(['lake', 'env', 'printenv', 'LEAN_PATH'], cwd=cwd)
-    return cwd, p
-
-if __name__ == '__main__':
-    project_path, lean_path = get_project_and_lean_path()
-    print(f"$PWD: {project_path}")
-    print(f"$LEAN_PATH: {lean_path}")
-    server = Server(imports=['Example'], project_path=project_path, lean_path=lean_path)
-    units, invocations = server.tactic_invocations(project_path / "Example.lean")
-    for i, u in enumerate(units):
-        print(f"==== #{i} ====")
-        print(u)
-    print("==== Invocations ====")
-    for i in invocations:
-        print(f"{i.before}\n{i.tactic}\n{i.after}\n")
diff --git a/examples/sketch.py b/examples/sketch.py
index 0f9bb74..f8cad14 100644
--- a/examples/sketch.py
+++ b/examples/sketch.py
@@ -32,5 +32,5 @@ theorem add_comm_proved_formal_sketch : ∀ n m : Nat, n + m = m + n := by
 
 if __name__ == '__main__':
     server = Server()
-    state0, = server.load_sorry(sketch)
-    print(state0)
+    unit, = server.load_sorry(sketch)
+    print(unit.goal_state)
diff --git a/pantograph/data.py b/pantograph/data.py
index d2c0ae0..5863aac 100644
--- a/pantograph/data.py
+++ b/pantograph/data.py
@@ -25,8 +25,10 @@ class TacticInvocation:
 @dataclass(frozen=True)
 class CompilationUnit:
 
+    # Byte boundaries [begin, end[ of each compilation unit.
     i_begin: int
     i_end: int
+
     messages: list[str] = field(default_factory=list)
 
     invocations: Optional[list[TacticInvocation]] = None