Functions

A function f is a mapping from X to Y:

• X is a nonempty set.
• Y is a nonempty set.

Every element in X maps to a unique element in Y.

We create a function if there are three plates of food (the plates are the three elements of Y) on a kitchen counter and three people come to the kitchen (the people are the three elements of X) and each person takes a plate.

Note that the last person didn’t get to make a choice. We will come across this in the idea of Degrees of Freedom.