There comes some point in teaching, where I have to introduce Coulomb's law in electricity. Here's where I always hit a dilemma: I give a series of sentences describing the properties of the Coulomb force. One sentence goes:

The force is inversely proportional to the square of the distance between them.

The issue: should I underline (or otherwise emphasize) "inversely" and "square"? Or should I underline "to" and "the"? In other words,