The original is unfaithful to the translation. -Jorge Luis Borges
Thornton CC. Coefficient of Restitution for Collinear Collisions of Elastic-Perfectly Plastic Spheres. J. Appl. Mech.. 1997;64(2):383-386. doi:10.1115/1.2787319.
What is light, and how can it travel in a vacuum forever