diff --git a/w1_topointro/1D.ipynb b/w1_topointro/1D.ipynb
index 51c991db098004611bb3d44b49f622af435bff27..0429b0bf0f1f81829077f5cdc68344073e634a99 100644
--- a/w1_topointro/1D.ipynb
+++ b/w1_topointro/1D.ipynb
@@ -3,7 +3,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "import sys\n",
@@ -92,7 +94,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "MoocVideo(\"U84MzZm9Gbo\", src_location='1.2-intro')"
@@ -182,7 +186,7 @@
     "\n",
     "Starting from this Hamiltonian, the unpaired Majorana regime is the special point $\\Delta=t$ and $\\mu=0$, while the completely trivial regime of isolated fermions is $\\Delta=t=0$ and $\\mu\\neq 0$.\n",
     "\n",
-    "As we learned just before, it is useful to write down the above superconducting Hamiltonian in the Bogoliubov-de Gennes formalism $H = \\tfrac{1}{2} C^\\dagger H_\\textrm{BdG} C$, with $C$ a column vector containing all creation and annihilation operators, $C=(c_1, \\dots, c_N, c_1^\\dagger, \\dots, c^\\dagger_N)^T$. The $2N\\times 2N$ matrix $H_\\textrm{BdG}$ can be written in a compact way by using Pauli matrices $\\tau$ in particle and hole space, and denoting with $\\left|n\\right\\rangle$ a column basis vector $(0,\\dots,1,0,\\dots)^T$ corresponding to the $n$-th site of the chain. In this way, we have for instance that $C^\\dagger\\,\\tau_z\\,\\left|n\\right\\rangle\\left\\langle n\\right|\\,C = 2c_n^\\dagger c_n$. The Bogoliubov-de Gennes Hamiltonian is then given by\n",
+    "As we learned just before, it is useful to write down the above superconducting Hamiltonian in the Bogoliubov-de Gennes formalism $H = \\tfrac{1}{2} C^\\dagger H_\\textrm{BdG} C$, with $C$ a column vector containing all creation and annihilation operators, $C=(c_1, \\dots, c_N, c_1^\\dagger, \\dots, c^\\dagger_N)^T$. The $2N\\times 2N$ matrix $H_\\textrm{BdG}$ can be written in a compact way by using Pauli matrices $\\tau$ in particle and hole space, and denoting with $\\left|n\\right\\rangle$ a column basis vector $(0,\\dots,1,0,\\dots)^T$ corresponding to the $n$-th site of the chain. In this way, we have for instance that $C^\\dagger\\,\\tau_z\\,\\left|n\\right\\rangle\\left\\langle n\\right|\\,C = 2c_n^\\dagger c_n-1$. The Bogoliubov-de Gennes Hamiltonian is then given by\n",
     "\n",
     "$$H_{BdG}=-\\sum_n \\mu \\tau_z\\left|n\\right\\rangle\\left\\langle n\\right|-\\sum_n \\left[(t\\tau_z+i\\Delta\\tau_y)\\,\\left|n\\right\\rangle\\left\\langle n+1 \\right| + \\textrm{h.c.}\\right].$$\n",
     "\n",
@@ -205,7 +209,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "def plot_wf(syst, wf1, wf2, lstyle='-', lcolor='b'):\n",
@@ -276,7 +282,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "question = (\"But wait! What happens if we remove the last Majorana site of a Kitaev chain\"\n",
@@ -359,7 +367,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "mus = np.arange(-3, 3, 0.25)\n",
@@ -490,7 +500,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "mus = np.arange(-3, 3, 0.25)\n",
@@ -548,7 +560,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "syst = kitaev_chain(L=25, periodic=True)\n",
@@ -578,7 +592,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "question = (\"What will happen if we take a 100 site Kitaev chain in the topological phase \" \n",
@@ -599,7 +615,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "MoocVideo(\"wiHPQlEha6g\", src_location='1.2-summary')"
@@ -608,7 +626,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "collapsed": true
+   },
    "outputs": [],
    "source": [
     "MoocDiscussion('Questions', 'Bulk-edge correspondence in the Kitaev chain')"