  In discrete convex analysis, various convexity concepts are considered for
discrete functions such as separable convexity, L-convexity, M-convexity,
integral convexity, and multimodularity. These concepts of discrete convex
functions are not mutually independent. For example, M-natural-convexity is a
special case of integral convexity, and the combination of L-natural-convexity
and M-natural-convexity coincides with separable convexity. This paper aims at
a fairly comprehensive analysis of the inclusion and intersection relations for
various classes of discrete convex functions. Emphasis is put on the analysis
of multimodularity in relation to L-natural-convexity and M-natural-convexity.
