  Mutual information is used as a purely geometrical regularization of
entanglement entropy applicable to any QFT. A coefficient in the mutual
information between concentric circular entangling surfaces gives a precise
universal prescription for the monotonous quantity in the c-theorem for d=3.
This is in principle computable using any regularization for the entropy, and
in particular is a definition suitable for lattice models. We rederive the
proof of the c-theorem for d=3 in terms of mutual information, and check our
arguments with holographic entanglement entropy, a free scalar field, and an
extensive mutual information model.
