Tuple

A set that can contain duplicates and directional order.

Cartesian Product

$\{1\} \times \{2, 3\} = \{<1, 2>, <1, 3>\}$

$|A \times B| = |A| \cdot |B|$

$\mathbb{R} \times \mathbb{R} = \mathbb{R}^2$