diff --git a/optimization202/Modeling_Session_1/completed_exercise_set1.ipynb b/optimization202/Modeling_Session_1/completed_exercise_set1.ipynb
index 025f6a5..3b34748 100755
--- a/optimization202/Modeling_Session_1/completed_exercise_set1.ipynb
+++ b/optimization202/Modeling_Session_1/completed_exercise_set1.ipynb
@@ -134,7 +134,7 @@
     "- If I invest in stock B, then I will invest in stock C.\n",
     "\n",
     "`Solution:`\n",
-    "Let $y_A, y_B, y_C$ be the three stocks.\n",
+    "Let $y_A, y_B, y_C \\in \\{0,1\\}$ be the three stocks.\n",
     "\\begin{align*}\n",
     "\\sum_{i \\in \\{A,B,C\\}} y_i &= 2 \\\\\n",
     "y_A &\\le y_B \\\\\n",