what is precession? can you please explain using different problems on it
Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle (nutation) is constant. In physics, there are two types of precession:torque-free and torque-induced.
In astronomy, "precession" refers to any of several slow changes in an astronomical body's rotational or orbital parameters, and especially to the Earth's precession of the equinoxes.
Precession of mercury
Mercury slows down in the slower time at its perihelion. This magnifies the effective curvature.
If time slows down so does light. So the propagation of gravity would also slow down along with such light slowdown. But it is only changes in gravity that will be seen to propagate.
There are no black holes because where time would stop gravity couldn't propagate.