Tuple

This is how AI think.

a1, a2, ..., an

This is n-tuple.
There are two sets such as (a1, a2, ..., an), (b1, b2, ..., bn), and (a1 = b1) ∧ (a2 = b2) ∧ ... ∧ (an = bn), which is called Cartesian product.

∴
a ∈ A, b ∈ B ⇒ (a, b) ∈ A × B

This is ordered pair. I use Python.

Moreover, this must be expansion.