The metric for gravitational plane waves has very high symmetry (two
spacelike commuting Killing vectors). For this high symmetry, a simple
renormalization of the lapse function is found which allows the constraint
algebra for canonical quantum gravity to close; also, the vector constraint has
the correct form to generate spatial diffeomorphisms. A measure is constructed
which respects the reality conditions, but does not yet respect the invariances
of the theory.Comment: 19 pages; LaTe