Commutative Law of Multiplication

Theorem
On all the standard number systems:
 * natural numbers $\N$
 * integers $\Z$
 * rational numbers $\Q$
 * real numbers $\R$
 * complex numbers $\C$

the operation of multiplication is commutative:


 * $a \times b = b \times a$

Proof
This is demonstrated in these pages:
 * Natural Number Multiplication is Commutative
 * Integer Multiplication is Commutative
 * Rational Multiplication is Commutative
 * Real Multiplication is Commutative
 * Complex Multiplication is Commutative