Definition:Neighborhood of Infinity (Real Analysis)/Negative Infinity

Definition
A neighborhood of $-\infty$ is a subset of the set of real numbers $\R$ wich contains an interval $(-\infty,a)$ for some $a\in\R$.

That is, a subset which contains all sufficiently large negative real numbers.

Also see

 * Definition:Neighborhood of Positive Infinity
 * Definition:Extended Real Number Line