Hello, I've just read and I think I have understood the following result : If we were to geodesically transport all points of a small 2D surface, so small that it would be flat for all purposes, in a direction vertically above it, and if this surface belongs in an arbitrary 3D manifold, then in general both its area and its shape will change. It is impossible to achieve a change in shape without its area to dwindle or expand simultaneously. And this is a property of the so-called Weyl tensor. I can somehow visualize how this is happening without recourse to advanced maths, but what a great result this is! In a 4D manifold, it is also true that the object can retain its volume even if the tidal forces (curvature) change its shape, but not in any lower dimension than 4. I have nothing more to ask, just to verify if this is true. What a great result! If it is true, it is a moment of revelation and enlightening for me.