[see also: look for, search
Here one seeks to minimize P(x) over the class of feedback controls.
In particular, integral curves evolve continuously, and we should seek to represent them using a measure which reflects this continuity in some way.
In applications of Theorem 1, we are usually seeking a lower bound for f(E).
Thus f is the function sought.
Therefore, the system (5) has a solution of the sought-for type.