diff --git a/Notebooks/Chap18/18_1_Diffusion_Encoder.ipynb b/Notebooks/Chap18/18_1_Diffusion_Encoder.ipynb
index 9cc076f..17656de 100644
--- a/Notebooks/Chap18/18_1_Diffusion_Encoder.ipynb
+++ b/Notebooks/Chap18/18_1_Diffusion_Encoder.ipynb
@@ -403,7 +403,7 @@
         "    marginal_at_time_t = np.zeros_like(pr_x_true);\n",
         "\n",
         "\n",
-        "    # TODO Write ths function\n",
+        "    # TODO Write this function\n",
         "    # 1. For each x (value in x_plot_vals):\n",
         "      # 2. Compute the mean and variance of the diffusion kernel at time t\n",
         "      # 3. Compute pdf of this Gaussian at every x_plot_val\n",