Hello my dear friend @stefano.massari. Certainly the cover image is very explicit, so anyone can clearly understand that the behavior of a gas at constant temperature makes the pressure inversely proportional to the volume, this means that if the volume decreases the pressure increases, and if the pressure decreases the volume increases, this is clearly seen in an embolo-piston system as shown in the figure.
The other important thing to highlight is how we can calculate the work generated by an expansion force of an ideal gas by means of integral calculus.
Greetings my dear friend and thanks for always supporting the interaction of my posts.