  In massive gravity and in bimetric theories of gravity, two constraints are
needed to eliminate the two phase-space degrees of freedom of the
Boulware-Deser ghost. For recently proposed non-linear theories, a Hamiltonian
constraint has been shown to exist and an associated secondary constraint was
argued to arise as well. In this paper we explicitly demonstrate the existence
of the secondary constraint. Thus the Boulware-Deser ghost is completely absent
from these non-linear massive gravity theories and from the corresponding
bimetric theories.
