diff --git a/1_numpy_matplotlib_scipy_sympy/1-numpy_tutorial_EN.ipynb b/1_numpy_matplotlib_scipy_sympy/1-numpy_tutorial_EN.ipynb
index 67f52f1..e533bb3 100644
--- a/1_numpy_matplotlib_scipy_sympy/1-numpy_tutorial_EN.ipynb
+++ b/1_numpy_matplotlib_scipy_sympy/1-numpy_tutorial_EN.ipynb
@@ -33,7 +33,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Introduction"
+    "## 1. Introduction"
    ]
   },
   {
@@ -67,7 +67,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Creating `numpy` arrays"
+    "## 2. Creating `numpy` arrays"
    ]
   },
   {
@@ -85,7 +85,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### From lists"
+    "### 2.1 From lists"
    ]
   },
   {
@@ -399,7 +399,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Using array-generating functions"
+    "### 2.2 Using array-generating functions"
    ]
   },
   {
@@ -758,14 +758,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## File I/O"
+    "## 3 File I/O"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Comma-separated values (CSV)"
+    "### 3.1 Comma-separated values (CSV)"
    ]
   },
   {
@@ -945,7 +945,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Numpy's native file format"
+    "### 3.2 Numpy's native file format"
    ]
   },
   {
@@ -1000,7 +1000,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## More properties of the numpy arrays"
+    "## 4. More properties of the numpy arrays"
    ]
   },
   {
@@ -1066,14 +1066,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Manipulating arrays"
+    "## 5. Manipulating arrays"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Indexing"
+    "### 5.1 Indexing"
    ]
   },
   {
@@ -1299,7 +1299,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Index slicing"
+    "### 5.2 Index slicing"
    ]
   },
   {
@@ -1626,7 +1626,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Fancy indexing"
+    "### 5.3 Fancy indexing"
    ]
   },
   {
@@ -1851,14 +1851,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Functions for extracting data from arrays and creating arrays"
+    "## 6. Functions for extracting data from arrays and creating arrays"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### where"
+    "### 6.1 where"
    ]
   },
   {
@@ -1914,7 +1914,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### diag"
+    "### 6.2 diag"
    ]
   },
   {
@@ -1968,7 +1968,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### take"
+    "### 6.3 take"
    ]
   },
   {
@@ -2071,7 +2071,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### choose"
+    "### 6.4 choose"
    ]
   },
   {
@@ -2108,7 +2108,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Linear algebra"
+    "## 7. Linear algebra"
    ]
   },
   {
@@ -2122,7 +2122,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Scalar-array operations"
+    "### 7.1Scalar-array operations"
    ]
   },
   {
@@ -2213,7 +2213,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Element-wise array-array operations"
+    "### 7.2 Element-wise array-array operations"
    ]
   },
   {
@@ -2318,7 +2318,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Matrix algebra"
+    "### 7.3 Matrix algebra"
    ]
   },
   {
@@ -2601,7 +2601,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Array/Matrix transformations"
+    "### 7.4 Array/Matrix transformations"
    ]
   },
   {
@@ -2811,7 +2811,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Matrix computations"
+    "### 7.5 Matrix computations"
    ]
   },
   {
@@ -2914,7 +2914,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Data processing"
+    "### 7.6 Data processing"
    ]
   },
   {
@@ -3225,7 +3225,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Computations on subsets of arrays"
+    "### 7.7 Computations on subsets of arrays"
    ]
   },
   {
@@ -3362,7 +3362,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Calculations with higher-dimensional data"
+    "### 7.8 Calculations with higher-dimensional data"
    ]
   },
   {
@@ -3471,7 +3471,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Reshaping, resizing and stacking arrays"
+    "## 8. Reshaping, resizing and stacking arrays"
    ]
   },
   {
@@ -3748,7 +3748,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Adding a new dimension: newaxis"
+    "## 9. Adding a new dimension: newaxis"
    ]
   },
   {
@@ -3889,7 +3889,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Stacking and repeating arrays"
+    "## 10. Stacking and repeating arrays"
    ]
   },
   {
@@ -3903,7 +3903,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### tile and repeat"
+    "### 10.1 tile and repeat"
    ]
   },
   {
@@ -4019,7 +4019,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### concatenate"
+    "### 10.2 concatenate"
    ]
   },
   {
@@ -4078,7 +4078,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### hstack and vstack"
+    "### 10.3 hstack and vstack"
    ]
   },
   {
@@ -4128,7 +4128,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Copy and \"deep copy\""
+    "## 11. Copy and \"deep copy\""
    ]
   },
   {
@@ -4281,7 +4281,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Iterating over array elements"
+    "## 12. Iterating over array elements"
    ]
   },
   {
@@ -4406,7 +4406,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Vectorizing functions"
+    "## 13. Vectorizing functions"
    ]
   },
   {
@@ -4587,7 +4587,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Using arrays in conditions"
+    "## 14. Using arrays in conditions"
    ]
   },
   {
@@ -4683,7 +4683,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Type casting"
+    "## 15. Type casting"
    ]
   },
   {
@@ -4783,7 +4783,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Further reading"
+    "## 16. Further reading"
    ]
   },
   {
@@ -4799,7 +4799,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Versions"
+    "## 17. Versions"
    ]
   },
   {
diff --git a/1_numpy_matplotlib_scipy_sympy/2-matplotlib_simple_tutorial_EN.ipynb b/1_numpy_matplotlib_scipy_sympy/2-matplotlib_simple_tutorial_EN.ipynb
index 91c18f4..f74796b 100644
--- a/1_numpy_matplotlib_scipy_sympy/2-matplotlib_simple_tutorial_EN.ipynb
+++ b/1_numpy_matplotlib_scipy_sympy/2-matplotlib_simple_tutorial_EN.ipynb
@@ -459,7 +459,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.5.2"
+   "version": "3.6.8"
   }
  },
  "nbformat": 4,
diff --git a/1_numpy_matplotlib_scipy_sympy/3-ipython_notebook.ipynb b/1_numpy_matplotlib_scipy_sympy/3-ipython_notebook.ipynb
index 503ee4a..009ba78 100644
--- a/1_numpy_matplotlib_scipy_sympy/3-ipython_notebook.ipynb
+++ b/1_numpy_matplotlib_scipy_sympy/3-ipython_notebook.ipynb
@@ -4,7 +4,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# 1.1. 介绍IPython和Jupyter笔记本"
+    "# 介绍IPython和Jupyter笔记本"
    ]
   },
   {
diff --git a/1_numpy_matplotlib_scipy_sympy/3-ipython_notebook_EN.ipynb b/1_numpy_matplotlib_scipy_sympy/3-ipython_notebook_EN.ipynb
index 1016538..880e420 100644
--- a/1_numpy_matplotlib_scipy_sympy/3-ipython_notebook_EN.ipynb
+++ b/1_numpy_matplotlib_scipy_sympy/3-ipython_notebook_EN.ipynb
@@ -4,7 +4,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# 1.1. Introducing IPython and the Jupyter Notebook"
+    "# Introducing IPython and the Jupyter Notebook"
    ]
   },
   {
@@ -330,7 +330,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.5.2"
+   "version": "3.6.8"
   }
  },
  "nbformat": 4,
diff --git a/1_numpy_matplotlib_scipy_sympy/4-scipy_tutorial.ipynb b/1_numpy_matplotlib_scipy_sympy/4-scipy_tutorial.ipynb
index dc332a8..bbcb3e9 100644
--- a/1_numpy_matplotlib_scipy_sympy/4-scipy_tutorial.ipynb
+++ b/1_numpy_matplotlib_scipy_sympy/4-scipy_tutorial.ipynb
@@ -34,7 +34,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 简介"
+    "## 1. 简介"
    ]
   },
   {
@@ -91,7 +91,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 特殊功能"
+    "## 2. 特殊功能"
    ]
   },
   {
@@ -194,14 +194,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 积分"
+    "## 3. 积分"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### 数值积分：求积"
+    "### 3.1 数值积分：求积"
    ]
   },
   {
@@ -379,7 +379,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 常微分方程 (ODEs)"
+    "## 4. 常微分方程 (ODEs)"
    ]
   },
   {
@@ -755,7 +755,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 傅立叶转换"
+    "## 5. 傅立叶转换"
    ]
   },
   {
@@ -873,7 +873,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 线性代数"
+    "## 6. 线性代数"
    ]
   },
   {
@@ -891,7 +891,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### 线性代数系统"
+    "### 6.1 线性代数系统"
    ]
   },
   {
@@ -1045,7 +1045,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### 特征值和特征向量"
+    "### 6.2 特征值和特征向量"
    ]
   },
   {
@@ -1181,7 +1181,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### 矩阵操作"
+    "### 6.3 矩阵操作"
    ]
   },
   {
@@ -1253,7 +1253,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### 稀疏矩阵"
+    "### 6.4 稀疏矩阵"
    ]
   },
   {
@@ -1648,7 +1648,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 优化"
+    "## 7. 优化"
    ]
   },
   {
@@ -1673,7 +1673,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### 找到最小值"
+    "### 7.1 找到最小值"
    ]
   },
   {
@@ -1836,7 +1836,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### 找到一个方程的解"
+    "### 7.2 找到一个方程的解"
    ]
   },
   {
@@ -1956,7 +1956,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 插值"
+    "## 8. 插值"
    ]
   },
   {
@@ -2033,7 +2033,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 统计"
+    "## 9. 统计"
    ]
   },
   {
@@ -2188,7 +2188,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### 统计测试"
+    "### 9.1 统计测试"
    ]
   },
   {
diff --git a/1_numpy_matplotlib_scipy_sympy/4-scipy_tutorial_EN.ipynb b/1_numpy_matplotlib_scipy_sympy/4-scipy_tutorial_EN.ipynb
index bfbf932..55b93ac 100644
--- a/1_numpy_matplotlib_scipy_sympy/4-scipy_tutorial_EN.ipynb
+++ b/1_numpy_matplotlib_scipy_sympy/4-scipy_tutorial_EN.ipynb
@@ -34,7 +34,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Introduction"
+    "## 1. Introduction"
    ]
   },
   {
@@ -91,7 +91,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Special functions"
+    "## 2. Special functions"
    ]
   },
   {
@@ -197,14 +197,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Integration"
+    "## 3. Integration"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Numerical integration: quadrature"
+    "### 3.1 Numerical integration: quadrature"
    ]
   },
   {
@@ -383,7 +383,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Ordinary differential equations (ODEs)"
+    "## 4. Ordinary differential equations (ODEs)"
    ]
   },
   {
@@ -757,7 +757,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Fourier transform"
+    "## 5. Fourier transform"
    ]
   },
   {
@@ -875,7 +875,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Linear algebra"
+    "## 6. Linear algebra"
    ]
   },
   {
@@ -894,7 +894,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Linear equation systems"
+    "### 6.1 Linear equation systems"
    ]
   },
   {
@@ -1048,7 +1048,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Eigenvalues and eigenvectors"
+    "### 6.2 Eigenvalues and eigenvectors"
    ]
   },
   {
@@ -1184,7 +1184,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Matrix operations"
+    "### 6.3 Matrix operations"
    ]
   },
   {
@@ -1256,7 +1256,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Sparse matrices"
+    "### 6.4 Sparse matrices"
    ]
   },
   {
@@ -1601,21 +1601,19 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 64,
+   "execution_count": 1,
    "metadata": {},
    "outputs": [
     {
-     "data": {
-      "text/plain": [
-       "array([[ 1.],\n",
-       "       [ 6.],\n",
-       "       [ 5.],\n",
-       "       [ 5.]])"
-      ]
-     },
-     "execution_count": 64,
-     "metadata": {},
-     "output_type": "execute_result"
+     "ename": "NameError",
+     "evalue": "name 'A' is not defined",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[0;31mNameError\u001b[0m                                 Traceback (most recent call last)",
+      "\u001b[0;32m<ipython-input-1-bae968ab7277>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;31m# sparse matrix - dense vector multiplication\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m \u001b[0mA\u001b[0m \u001b[0;34m*\u001b[0m \u001b[0mv\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[0;31mNameError\u001b[0m: name 'A' is not defined"
+     ]
     }
    ],
    "source": [
@@ -1651,7 +1649,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Optimization"
+    "## 7. Optimization"
    ]
   },
   {
@@ -1676,7 +1674,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Finding a minima"
+    "### 7.1 Finding a minima"
    ]
   },
   {
@@ -1839,7 +1837,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Finding a solution to a function"
+    "### 7.2 Finding a solution to a function"
    ]
   },
   {
@@ -1959,7 +1957,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Interpolation"
+    "## 8. Interpolation"
    ]
   },
   {
@@ -2036,7 +2034,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Statistics"
+    "## 9. Statistics"
    ]
   },
   {
@@ -2191,7 +2189,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Statistical tests"
+    "### 9.1 Statistical tests"
    ]
   },
   {
@@ -2415,7 +2413,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.5.2"
+   "version": "3.6.8"
   }
  },
  "nbformat": 4,
diff --git a/1_numpy_matplotlib_scipy_sympy/5-sympy_tutorial.ipynb b/1_numpy_matplotlib_scipy_sympy/5-sympy_tutorial.ipynb
index 9567372..b6783b0 100644
--- a/1_numpy_matplotlib_scipy_sympy/5-sympy_tutorial.ipynb
+++ b/1_numpy_matplotlib_scipy_sympy/5-sympy_tutorial.ipynb
@@ -2412,7 +2412,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 11. 进一步的阅读"
+    "## 进一步的阅读"
    ]
   },
   {
@@ -2428,7 +2428,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## 12. 版本"
+    "## 版本"
    ]
   },
   {
diff --git a/1_numpy_matplotlib_scipy_sympy/5-sympy_tutorial_EN.ipynb b/1_numpy_matplotlib_scipy_sympy/5-sympy_tutorial_EN.ipynb
index c4de80e..fdf3d2a 100644
--- a/1_numpy_matplotlib_scipy_sympy/5-sympy_tutorial_EN.ipynb
+++ b/1_numpy_matplotlib_scipy_sympy/5-sympy_tutorial_EN.ipynb
@@ -32,7 +32,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Introduction"
+    "## 1. Introduction"
    ]
   },
   {
@@ -85,7 +85,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Symbolic variables"
+    "## 2. Symbolic variables"
    ]
   },
   {
@@ -232,7 +232,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Complex numbers"
+    "### 2.1 Complex numbers"
    ]
   },
   {
@@ -319,7 +319,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Rational numbers"
+    "### 2.2 Rational numbers"
    ]
   },
   {
@@ -419,7 +419,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Numerical evaluation"
+    "## 3. Numerical evaluation"
    ]
   },
   {
@@ -710,7 +710,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Algebraic manipulations"
+    "## 4. Algebraic manipulations"
    ]
   },
   {
@@ -724,7 +724,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Expand and factor"
+    "### 4.1 Expand and factor"
    ]
   },
   {
@@ -880,7 +880,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Simplify"
+    "### 4.2 Simplify"
    ]
   },
   {
@@ -972,7 +972,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### apart and together"
+    "### 4.3 apart and together"
    ]
   },
   {
@@ -1141,7 +1141,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Calculus"
+    "## 5. Calculus"
    ]
   },
   {
@@ -1155,7 +1155,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Differentiation"
+    "### 5.1 Differentiation"
    ]
   },
   {
@@ -1332,7 +1332,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Integration"
+    "## 5.2 Integration"
    ]
   },
   {
@@ -1468,7 +1468,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Sums and products"
+    "### 5.3 Sums and products"
    ]
   },
   {
@@ -1607,7 +1607,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Limits"
+    "## 6. Limits"
    ]
   },
   {
@@ -1802,7 +1802,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Series"
+    "## 7. Series"
    ]
   },
   {
@@ -2075,14 +2075,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Linear algebra"
+    "## 8. Linear algebra"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Matrices"
+    "### 8.1 Matrices"
    ]
   },
   {
@@ -2282,7 +2282,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Solving equations"
+    "## 9. Solving equations"
    ]
   },
   {
@@ -2526,7 +2526,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.5.2"
+   "version": "3.6.8"
   }
  },
  "nbformat": 4,