Definition:Darboux Function

Definition
Let $S \subseteq \R$.

Let $f: S \to \R$ be a real function.

Then $f$ is Darboux, given any $a, b \in S$ and $y \in \R$ such that $a < b$ and $y$ is between $\map f a$ and $\map f b$, there exists a $c \in S$ such that $a \le c \le b$ and $\map f c = y$.

That is, for every intermediate value between $\map f a$ and $\map f b$, that value is the image of some intermediate value between $a$ and $b$.

Also known as
$f$ is said to have the intermediate value property (frequently abbreviated as I.V.P.) $f$ is a Darboux function.