Gravitational waves and lensing in the metric theory proposed by Sobouti

We show that the metric f(R) theory of gravitation proposed by Sobouti (2007) predicts the existence of gravitational waves travelling at the speed of light in vacuum. In fact, this is prooved in general terms for all metric theories of gravity which can be expressed as powers of Ricci's scalar R. We also show that an extra additional lensing as compared to that predicted by standard general relativity is produced in that theory