Complex sentence: The Coulomb potential of electromagnetism is an example of a Yukawa potential with e − "kmr" equal to 1 everywhere; this is taken to mean that the photon mass "m" is equal to 0.
Split into simpler sentences: The Coulomb potential of electromagnetism is an example of a Yukawa potential with e − "kmr" equal to 1 everywhere. This can be interpreted as saying that the photon mass "m" is equal to 0.