Continuous Image of Connected Space is Connected/Corollary 3

Corollary to Continuous Image of Connected Space is Connected
Let $\mathbb I = \left[{a \,.\,.\, b}\right]$ be a closed real interval.

Let $f: \mathbb I \to \R$ be a continuous mapping.

Then $f$ has the intermediate value property.

Proof
From Only Intervals are Connected, $\mathbb I$ is connected.

By Continuous Image of Connected Space is Connected: corollary 2, $f \left({\mathbb I}\right)$ is also connected.

So from Only Intervals are Connected $f \left({\mathbb I}\right)$ is an real interval.

The result follows by definition of an real interval and the I.V.P..