Peres metric

In mathematical physics, the Peres metric is defined by the proper time
for any arbitrary function "f". If "f" is a harmonic function with respect to "x" and "y", then the corresponding Peres metric satisfies the Einstein field equations in vacuum. Such a metric is often studied in the context of gravitational waves. The metric is named for Israeli physicist Asher Peres, who first defined the metric in 1959.