Relations
If we have two sets, A and B, we can refer to the 'Cartesian Product' as being A x B. This means that if A = {1, 2, 3} and B = {a, b, c}, then A x B = {1a, 1b, 1c, 2a, 2b, 2c, 3a, 3b, 3c}. It's the set of all pairs of values where the first is from A and the second is from B.
A relation from A to B is a subset of A x B. A relation can be said to connect values together, in a way, showing a relationship between them.
