  The combination of the Lorentz symmetry and the strong subadditive property
of the entropy leads to a c-theorem for the entanglement entropy in 1+1
dimensions. We present a simple derivation of this theorem and compare the
associated c-functions with the Zamolodchikov's ones for the case of free
fields. We discuss the various difficulties which obstacle the naive
generalizations of the entropic c-theorem to higher dimensions.
