f Implicit MZO

In spite of the large effort devoted to the definition and implementation of more accurate migration to zero offset, or MZO operators, DMO remains in wide use. This is because DMO has two great advantages. Firstly, 3D DMO is just 2D DMO rotated according to the azimuth and secondly, DMO does not require us to specify a velocity model. However 3D MZO, even for a constant velocity gradient, corresponds to a full saddle operator which only works well if the actual velocities closely follow the specified gradient.