Natural Numbers under Addition do not form Group

Theorem
The algebraic structure $\struct {\N, +}$ consisting of the set of natural numbers $\N$ under addition $+$ is not a group.

Proof
From Natural Numbers under Addition form Commutative Monoid, $\struct {\N, +}$ has an identity element $0$.

However, for any $x \in \N$ such that $x \ne 0$ there exists no $y \in \N$ such that $x + y = 0$.

Thus the general element of $\struct {\N, +}$ has no inverse.

Hence the result by definition of group.