SESSION 2

*Sets, maps and composition*

**1. Review of Article I**

Before discussing some of the exercises in Article **I**, let’s have a quick review. A **set** is any collection of things. You know examples of infinite sets, like the set of all natural numbers, {0,1,2,3,…}, but we’ll take most of our examples from finite sets. Here is a typical **internal diagram** of a **function,** or **map:**

Other words that mean the same as *function* and *map* are **transformation, operator, morphism,** and **functional;** the idea is so important that it has been rediscovered and renamed in many different contexts.

As the internal diagram suggests, to have a **map** *f* **of sets** involves three things: ...

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