We present a derivation of a formula that gives dynamics of an integrable
cellular automaton associated with crystal bases. This automaton is related to
type D affine Lie algebra and contains usual box-ball systems as a special
case. The dynamics is described by means of such objects as carriers,
particles, and antiparticles. We derive it from an analysis of a recently
obtained formula of the combinatorial R (an intertwiner between tensor products
of crystals) that was found in a study of geometric crystals.Comment: LaTeX, 21 pages, 2 figure