diff --git a/exercises/ex02_solution/anharmonic.ipynb b/exercises/ex02_solution/anharmonic.ipynb
index cd7812173f3190735f39c747f001bf71e3f034b0..da89b03e4417821aecfbf575756d74ef77fe800f 100644
--- a/exercises/ex02_solution/anharmonic.ipynb
+++ b/exercises/ex02_solution/anharmonic.ipynb
@@ -26,22 +26,22 @@
     "\\end{equation}\n",
     "\n",
     "Let us now expand the $(a+a^{\\dagger})^4$ using the commutator relation $[a,a^{\\dagger}] = a a^{\\dagger} - a^{\\dagger} a = 1$ and the identity $a^{\\dagger} a = \\hat n$:\n",
-    "\\begin{align}\n",
+    "$$\\begin{align}\n",
     " ( a + a^{\\dagger})^4  &=  (a a + a a^{\\dagger} + a^{\\dagger} a + a^{\\dagger} a^{\\dagger})^2 \\\\\n",
     "  &=  ( a a + 2 a^{\\dagger} a + 1 + a^{\\dagger} a^{\\dagger})^2 \\\\\n",
     "  &=  a^4 + 2 a a \\hat n + 2 a a + 2 \\hat n a a + 6 \\hat n^2 + 6 \\hat n + 3 + 2 \\hat n a^{\\dagger} a^{\\dagger} \\\\\n",
     "  &\\quad + 2 a^{\\dagger} a^{\\dagger} \\hat n + 2 a^{\\dagger} a^{\\dagger} + (a^{\\dagger})^4\n",
-    "\\end{align}\n",
+    "\\end{align}$$\n",
     "\n",
     "Using $a | n \\rangle = \\sqrt{n} | n -1 \\rangle$, $ a^{\\dagger} | n \\rangle = \\sqrt{n+1} | n+1 \\rangle$ and $ \\langle m | n \\rangle = \\delta_{m,n}$\n",
     "we obtain following non-zero matrix elements:\n",
-    "\\begin{align}\n",
+    "$$\\begin{align}\n",
     "    \\langle n | 6 \\hat n^2 + 6 \\hat n + 3 | n \\rangle &= 6 n^2 + 6 n + 3 \\\\\n",
     "    \\langle n + 2 | 2 \\hat n a^{\\dagger} a^{\\dagger} + 2 a^{\\dagger} a^{\\dagger} + 2 a^{\\dagger} a^{\\dagger} \\hat n | n \\rangle & = \\langle n | 2 a a \\hat n + 2 a a + 2 \\hat a a | n + 2\\rangle \\\\\n",
     "    & =(4 n + 6) \\sqrt{ (n+1) (n+2) } \\\\\n",
     "    \\langle n + 4 | (a^{\\dagger})^4 | n \\rangle & = \\langle n | a^4 | n+4 \\rangle \\\\\n",
     "    & = \\sqrt{(n+1) \\cdot (n+2) \\cdot (n+3) \\cdot (n+4)}\n",
-    "\\end{align}\n",
+    "\\end{align}$$\n",
     "\n",
     "A solution code setting up and diagonalizing a matrix for a given cutoff $N$ is given below.\n",
     "The dependence of the  energy spectrum on the anharmonicity $K$ is shown in figure at the bottom.\n",
@@ -188,7 +188,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.3"
+   "version": "3.4.4"
   }
  },
  "nbformat": 4,