  A d.c. (delta-convex) function on a normed linear space is a function
representable as a difference of two continuous convex functions. We show that
an infinite dimensional analogue of Hartman's theorem on stability of d.c.
functions under compositions does not hold in general. However, we prove that
it holds in some interesting particular cases. Our main results about
compositions are proved in the more general context of d.c. mappings between
normed linear spaces.
