Integers under Multiplication form Monoid

Theorem

The set of integers under multiplication $\struct {\Z, \times}$ is a monoid.

Proof

From Integers under Multiplication form Semigroup, $\struct {\Z, \times}$ is a semigroup.

From Integer Multiplication Identity is One, $\struct {\Z, \times}$ has an identity element, which is $1$.

All the criteria for being a monoid are thus seen to be fulfilled.

$\blacksquare$