diff --git a/Chapters/15-Appendix-A/INDEX.md b/Chapters/15-Appendix-A/INDEX.md
new file mode 100644
index 0000000..11ec8f8
--- /dev/null
+++ b/Chapters/15-Appendix-A/INDEX.md
@@ -0,0 +1,22 @@
+# Appendix A
+
+## Laplace Operator[^khan-1]
+
+It is defined as $\nabla \cdot \nabla f \in \R$ and is equivalent to the
+**divergence of the function**. Technically speaking it gives us the
+**magnitude of a local maximum or minimum**.
+
+Positive values mean that we are around a local maximum and vice-versa. The
+higher the magnitude, the higher (or lower) is the local maximum (or minimum).
+
+Another way to see this is as the divergence of the function that tells us whether
+that is a point of attraction or divergence.
+
+It can also be used to compute the net flow of particles in that region of space
+
+> [!CAUTION]
+> This is not a **discrete laplace operator**, which is instead a **matrix** here,
+> as there are many other formulations.
+
+[^khan-1]: [Khan Academy | Laplace Intuition | 9th November 2025](https://www.youtube.com/watch?v=EW08rD-GFh0)
+