Let us consider the optimal control problem formulated in Section 3.3 and adopt as standing assumptions all the regularity requirements imposed in that section on the control system and the cost functional. We will now describe two special instances of this optimal control problem, for which we want to state and then (in Section 4.2) prove the maximum principle. Afterwards (in Section 4.3.1) we will explain how the maximum principle for other cases of interest can be deduced from these two special results.