# How to prove Bossert inequality for the symbol error probability?

In the book : Coding theory-Algorithms, Architectures and Applications p.20, the authors have introduced the following inequality ( and precised that it was taken from Bossert's Channel Coding for telecommunications ):

$$\frac {P_{err}}{k} \leq P_{Sym} \leq P_{err}$$

Where $$P_{err}$$ is the word error probability and $$P_{Sym}$$ is the average symbol error probability.

While the rightmost inequality is intuitive, I cannot fathom the left side.