In classical analysis, there is a vast difference between the class of
problems that may be handled by means of the methods of calculus and the
class of problems requiring combinatorial techniques. With the advent of
the digital computer, the distinction begins to blur, and with the
increasing emphasis on problems involving optimization over structures,
tIlE' distinction vanishes. What is necessary for the analytic and
computational treatment of significant questions arising in modern
control theory, mathematical economics, scheduling theory, operations
research, bioengineering, and so forth is a new and more flexible
mathematical theory which subsumes both the cla8sical continuous and
discrete t 19orithms. The work by HAMMER (IVANESCU) and RUDEANU on
Boolean methods represents an important step in this dnectlOn, and it is
thus a great pleasure to welcome it into print. It will certainly
stimulate a great deal of additional research in both theory and
application. RICHARD BELLMAN University of Southern California FOf(, WOl