there are four lights [ci skip]

Author: minrk

docs/source/examples/Notebook/What is the Jupyter Notebook.ipynb

@@ -142,11 +142,10 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Notebooks consist of a **linear sequence of cells**. There are four basic cell types:\n",
+    "Notebooks consist of a **linear sequence of cells**. There are three basic cell types:\n",
     "\n",
     "* **Code cells:** Input and output of live code that is run in the kernel\n",
     "* **Markdown cells:** Narrative text with embedded LaTeX equations\n",
-    "* **Heading cells:** Jupyter no longer uses special heading cells. Instead, write your headings in Markdown cells using # characters\n",
     "* **Raw cells:** Unformatted text that is included, without modification, when notebooks are converted to different formats using nbconvert\n",
     "\n",
     "Internally, notebook documents are **[JSON](https://en.wikipedia.org/wiki/JSON) data** with **binary values [base64](http://en.wikipedia.org/wiki/Base64)** encoded. This allows them to be **read and manipulated programmatically** by any programming language. Because JSON is a text format, notebook documents are version control friendly.\n",