Subring of Integers is Ideal

Theorem

Let $\struct {\Z, +}$ be the additive group of integers.


Every subring of $\struct {\Z, +, \times}$ is an ideal of the ring $\struct {\Z, +, \times}$.


Proof

Follows directly from:

Subrings of Integers are Sets of Integer Multiples

and:

Subgroup of Integers is Ideal.

$\blacksquare$


Sources

  • 1970: B. Hartley and T.O. Hawkes: Rings, Modules and Linear Algebra ... (previous) ... (next): $\S 2.3$: Some properties of subrings and ideals
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