Daniel Liberzon
Since the building of the universe is perfect and is created by the wisdom creator, nothing arises in the universe in which one cannot see the sense of some maximum or minimum.
Leonhard Euler
The words ``control theory'' are, of course, of recent origin, but the subject itself is much older, since it contains the classical calculus of variations as a special case, and the first calculus of variations problems go back to classical Greece.
Hector J. Sussmann
Cover illustration by Polina Ben-Sira ©2009