It is a well-known fact that $\mathbb{Z}$ is not definable in the structure $\mathcal{R}=(\mathbb{R}, +, -, < , 0, 1)$. This follows from Tarski's quantifier elimination, and in fact we can conclude that the structure 
$\mathcal{R}$ is an o-minimal structure.

>**Question.** Is there a more direct proof of the above undefinability result?

I essentially mean a proof which does not use the above result of Tarski or its variants. 

In general, what other different proofs of the above result exist?
Providing references is appreciated.