# Piecewise-linear activation function definition doesn't correspond to graph found in textbook

This question is a duplicate of this question on StackOverflow, but it hasn't been answered in 2 years, which is why I'm re-posting it. If this isn't an appropriate way to go about this, please let me know as I'm new to the community.

The piecewise-linear activation function as defined in Neural Networks by Simon S. Haykin has three pieces, one of which is:

$$φ(v) = v, -0.5 < v < 0.5$$

Haykin presents this graph of the function:

in which $$φ(v)$$ increases linearly w.r.t. $$v$$ in the region $$-0.5.

As far as I can tell, this graph doesn't describe the function above. For example, for $$v = 0$$, $$φ(v) = 0.5$$ instead of $$0$$. In fact, it seems that the actual definition of $$φ(v)$$ in that region is $$φ(v) = v + 0.5$$.

This mistake seems so obvious that I must be missing something.