The letter is devoted to establishing an elementary theorem of relativistic mechanics which has so far escaped attention and hopes to illustrate the difference between the various potentials in relativistic mechanics, a point too often overlooked.
Pietenpol, J. N., & Speiser, D. (1971). Unnoticed theorem of relativistic mechanics. Nature. Physical Science, 229(7), 199-200. https://hdl.handle.net/2078.5/67566 (Original work published 1971)