diff --git a/examples/RectangularPeriodicity.ipynb b/examples/RectangularPeriodicity.ipynb
index 2b6e0e8..2f77429 100644
--- a/examples/RectangularPeriodicity.ipynb
+++ b/examples/RectangularPeriodicity.ipynb
@@ -19,6 +19,10 @@
         "\n",
         "$M_{k_1, k_2}(n_1, n_2) = \\exp \\big(2 \\pi i \\big(\\frac{1}{N_1}n_1 (k_1 - k_2/2) + \\frac{1}{N_2}n_2 k_2\\big)\\big)$\n",
         "\n",
+        "The FFT implemented here is as described in\n",
+        "\n",
+        "> J. C. Ehrhardt, “Hexagonal fast Fourier transform with rectangular output,” IEEE Transactions on Signal Processing, vol. 41, no. 3. Institute of Electrical and Electronics Engineers (IEEE), pp. 1469–1472, Mar. 1993. doi: 10.1109/78.205759. \n",
+        "\n",
         "Here we demonstrate the `fft` and `ifft` for rectangular periodicity. Let's plot the (1, 1) mode."
       ]
     },
@@ -357,7 +361,8 @@
       "name": "python3"
     },
     "language_info": {
-      "name": "python"
+      "name": "python",
+      "version": "3.10.14"
     }
   },
   "nbformat": 4,