Cartesian Products
We have a definition for the cartesian product of two sets, but we can extend this definition.
We have a definition for the cartesian product of two sets, but we can extend this definition.
Let \mathcal{A} be a nonempty collection of sets.
An indexing function on \mathcal{A} is a surjective function f from some set J, called the index set, to \mathcal{A}.
The collection \mathcal{A} with the indexing function f is called an [indexed family of sets]