ABSTRACT
This chapter is entirely devoted to the study of duality in systems with a predominantly combinatorial structure, specifically, that of a graph. Almost all, except the latter half of the first section, is based on material taken from the book "Network Flows and Monotropic Optimization" by R.T. Rockafellar [R3]. Both authors have had the fortunate opportunity of learning much about duality from this book when we were asked to teach it to undergraduate students at the honours level. We have since been convinced that the study of network problems is the best, if not the easiest, way of understanding duality, both from a geometric as well as an algebraic perspective.
