Questions

The lymphatic system is a complex system of fluid drainage and transport, and immune response and disease resistance. Fluid that is forced out of the bloodstream during normal circulation is filtered through lymph nodes to remove bacteria, abnormal cells and other matter. This fluid is then transported back into the bloodstream via the lymph vessels. Lymph only moves in one direction, toward the heart.

There is no difference except for the fact that the first one gives a hint that the function fun() is probably in another source file.

In vacuum and in homogeneous, transparent media, such as air, water, and glass, light moves in a straight line. When light encounters a boundary between two different transparent media, some light is reflected and some moves from the first into the second medium.