Submodular functions: reference request I would be very much interested in references to the theory of submodular functions (from basics to advanced).

In particular, I am studying approximations to hard optimization problems and I want to develop my foundations in submodular functions as they are relevant to the optimization problems I have been studying.

Thanks in advance.
The references I use (and like) are selected chapters in Schrijver's 3-volume Combinatorial Optimization: Polyhedra and Efficiency (Springer) and Vygen's Combinatorial Optimization (Springer). There is a book devoted to submodular functions by Fujishige: Submodular Functions and Optimization, volume 58 of Annals of Discrete Mathematics, North-Holland (2nd edition from 2005).