Well-posed initial-boundary value problem for the harmonic Einstein equations using energy estimates

In recent work, we used pseudo-differential theory to establish conditions that the initial-boundary value problem for second-order systems of wave equations be strongly well-posed in a generalized sense. The applications included the harmonic version of the Einstein equations. Here we show that these results can also be obtained via standard energy estimates, thus establishing strong well-posedness of the harmonic Einstein problem in the classical sense.