Additive Group of Integers is Subgroup of Reals

Theorem
Let $\left({\Z, +}\right)$ be the Additive Group of Integers.

Let $\left({\R, +}\right)$ be the Additive Group of Real Numbers.

Then $\left({\Z, +}\right)$ is a normal subgroup of $\left({\R, +}\right)$.

Proof
From Additive Group of Integers Subgroup of Rationals, $\left({\Z, +}\right) \triangleleft \left({\Q, +}\right)$.

From Additive Group of Rationals Subgroup of Reals, $\left({\Q, +}\right) \triangleleft \left({\R, +}\right)$.

Thus $\left({\Z, +}\right) \le \left({\R, +}\right)$.

As the Additive Group of Real Numbers is abelian, from All Subgroups of Abelian Group are Normal it follows that $\left({\Z, +}\right) \triangleleft \left({\R, +}\right)$.