Intersection of Open Intervals of Positive Reals is Empty

Theorem
Let $\R_{>0}$ be the set of strictly positive real numbers.

For all $x \in \R_{>0}$, let $A_x$ be the open real interval $\openint 0 x$.

Then:
 * $\ds \bigcap_{x \mathop \in \R_{>0} } A_x = \O$

Proof
Let $\ds A = \bigcap_{x \mathop \in \R_{>0} } A_x$.

$A \ne \O$.

Then:
 * $\exists y \in \R_{>0}: y \in A$

By definition of open interval:
 * $y \notin \openint 0 y = A_y$

and so by definition of intersection of family:
 * $y \notin A$

From this contradiction it follows that $A$ has no elements.

That is:
 * $\ds \bigcap_{x \mathop \in \R_{>0} } A_x = \O$