diff --git a/src/2_debye_model.md b/src/2_debye_model.md
index be8175344ced9b51cbde1ea645f92bb2c4ae9f30..744e7ee230f75af41aa1aff4d9fcaa82b54e498e 100644
--- a/src/2_debye_model.md
+++ b/src/2_debye_model.md
@@ -131,18 +131,18 @@ draw_classic_axes(ax, xlabeloffset=0.3)
 
 ## Exercises
 
-### Debye model: concepts
-a) Describe the concepts of k-space and density of states.
-b) Calculate the density of state $g(\omega)$ and $g(k)$  for a 3D, 2D and 1D systems with linear dispersion $\omega=vk$.
-c) _draft: sketch the state of a standing wave. Here I'm not sure what you exactly want to see, Anton, and how to write it down in an easy way._
-
-### Debye model in 2D
-a) State the assumptions of the Debye theory.
-b) Determine the energy of a two-dimensional solid as a function of $T$ using the Debye approximation (the integral can't be solved analytically).
-c) Calculate the heat capacity in the limit of high $T$ (hint: it goes to a constant).
-d) At low $T$, show that $C_V=KT^{n}$. Find $n$. Find $K$ in term of a definite integral.
-
-### Anisotropic velocities _this exercise looks a bit too hard in the end_
+### Exercise 1: Debye model: concepts
+1. Describe the concepts of k-space and density of states.
+2. Calculate the density of state $g(\omega)$ and $g(k)$  for a 3D, 2D and 1D systems with linear dispersion $\omega=vk$.
+3. _draft: sketch the state of a standing wave. Here I'm not sure what you exactly want to see, Anton, and how to write it down in an easy way._
+
+###  Exercise 2: Debye model in 2D
+1. State the assumptions of the Debye theory.
+2. Determine the energy of a two-dimensional solid as a function of $T$ using the Debye approximation (the integral can't be solved analytically).
+3. Calculate the heat capacity in the limit of high $T$ (hint: it goes to a constant).
+4. At low $T$, show that $C_V=KT^{n}$. Find $n$. Find $K$ in term of a definite integral.
+
+###  Exercise 3: Anisotropic velocities
 During the lecture we derived the low-temperature heat capacity assuming that the longitudinal and transverse modes have the same sound velocity $v$.
-a) Suppose that the longitudinal and transverse sound velocities are different ($v_L != v_T$). How does this change the Debye result?
-b) Suppose now that the velocity is anisotropic ($v_x!=v_y!=v_z$), neglecting the difference between transverse and longitudinal modes. How does this change the Debye result?
+1. Suppose that the longitudinal and transverse sound velocities are different ($v_L != v_T$). How does this change the Debye result?
+2. Suppose now that the velocity is anisotropic ($v_x!=v_y!=v_z$), neglecting the difference between transverse and longitudinal modes. How does this change the Debye result?