Inversion of a "discontinuous coordinate transformation" in general relativity

As early as 1972, Penrose - in a purely formal way - introduced a "discontinuous coordinate transformation", which relates a continuous representation of the metric of impulsive pp-waves to a discontinuous one. On the basis of the invertibility concept for generalized functions developed recently by the first author, we show that this discontinuous coordinate transformation indeed represents an invertible generalized function in the appropriate sense.