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    "# Chapter 4: Recursion & Looping (TL;DR)"
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    "**Iteration** is about **running blocks of code repeatedly**.\n",
    "\n",
    "There are two redundant approaches to achieving that.\n",
    "\n",
    "First, we combine functions that call themselves with conditional statements. This concept is known as **recursion** and suffices to control the flow of execution in *every* way we desire. For a beginner, this approach of **backward** reasoning might not be intuitive, but it turns out to be a handy tool to have in one's toolbox.\n",
    "\n",
    "Second, the `while` and `for` statements are alternative and potentially more intuitive ways to express iteration as they correspond to a **forward** reasoning. The `for` statement is **syntactic sugar** that allows rewriting common occurrences of the `while` statement concisely. Python provides the `break` and `continue` statements as well as an optional `else`-clause that make working with the `for` and `while` statements even more convenient.\n",
    "\n",
    "**Iterables** are any **concrete data types** that support being looped over, for example, with the `for` statement. The idea behind iterables is an **abstract concept** that may or may not be implemented by any given concrete data type. For example, both `list` and `range` objects can be looped over. The `list` type is also a **container** as any given `list` objects \"contains\" references to other objects in memory. On the contrary, the `range` type does not reference any other object but instead creates *new* `int` objects \"on the fly\" (i.e., when being looped over)."
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