Integer Multiplication is Commutative

Theorem
Integer multiplication is commutative:

$$\left[\!\left[{a, b}\right]\!\right]_\boxminus \times \left[\!\left[{c, d}\right]\!\right]_\boxminus = \left[\!\left[{c, d}\right]\!\right]_\boxminus \times \left[\!\left[{a, b}\right]\!\right]_\boxminus$$

Proof
From Natural Numbers form Semiring, we take it for granted that addition and multiplication are commutative on the natural numbers $$\N$$.

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