  Studies of new hyperbolic systems for the Einstein evolution equations show
that the ``slicing density'' $\alpha(t,x)$ can be freely specified while the
lapse $N = \alpha g^{1/2}$ cannot. Implementation of this small change in the
Arnowitt-Deser-Misner action principle leads to canonical equations that agree
with the Einstein equations whether or not the constraints are satisfied. The
constraint functions, independently of their values, then propagate according
to a first order symmetric hyperbolic system whose characteristic cone is the
light cone. This result follows from the twice-contracted Bianchi identity and
constitutes the central content of the constraint ``algebra'' in the canonical
formalism.
