“…where r j denotes the position vector of particle j in 3D-space, m j is its positive mass, G is the positive constant of universal gravitation, r lj = |r l − r j | is the distance between particles j and l, and e j is the charge of particle j such that m j = |e j |, with two possible choices of sign for the charge. In the mathematical literature we have found some papers in the context of determining Four-Body central configurations that consider negative masses [3], [4], [5], with a different equation of motion, a different definition of central configuration and without distinguishing between masses and charges. The difference with respect to the differential equation of motion used in those papers is stressed in an Appendix at the end of the paper, where, assuming the validity of Newton's second and third laws, the equation of motion used by those Authors is shown to produce, for a system of two masses of equal magnitude but different inertial and gravitational sign, a rigid body which is self-accelerated under no external force, violating Newton's first law expressing that a body subject to no external forces moves with constant velocity.…”