  As first shown by H. S. Green in 1952, the entropy of a classical fluid of
identical particles can be written as a sum of many-particle contributions,
each of them being a distinctive functional of all spatial distribution
functions up to a given order. By revisiting the combinatorial derivation of
the entropy formula, we argue that a similar correlation expansion holds for
the entropy of a crystalline system. We discuss how one- and two-body entropies
scale with the size of the crystal, and provide fresh numerical data to check
the expectation, grounded on theoretical arguments, that both entropies are
extensive quantities.
