"**Sequences** are an *abstract* concept that summarizes *four* behaviors an object may or may not exhibit. Sequences are\n",
"- **finite** and\n",
"- **ordered**\n",
"- **containers** that we may\n",
"- **loop over**.\n",
"\n",
"Examples are the `list`, `tuple`, but also the `str` types.\n",
"\n",
"Objects that exhibit all behaviors *except* being ordered are referred to as **collections**.\n",
"\n",
"The objects inside a sequence are called its **elements** and may be labeled with a unique **index**, an `int` object in the range $0 \\leq \\text{index} < \\lvert \\text{sequence} \\rvert$.\n",
"\n",
"`list` objects are **mutable**. That means we can change the references to the other objects it contains, and, in particular, re-assign them.\n",
"\n",
"On the contrary, `tuple` objects are like **immutable** lists: We can use them in place of any `list` object as long as we do *not* need to mutate it. Often, `tuple` objects are also used to model **records** of related **fields**."
