Blum, Alexander S. and Rickles, Dean (2018). Alfred Schild (1948): Discrete Space-Time and Integral Lorentz Transformations. In: Quantum Gravity in the First Half of the Twentieth Century: A Sourcebook. Berlin: Max-Planck-Gesellschaft zur Förderung der Wissenschaften.
Alfred Schild (1948). Discrete Space-Time and Integral Lorentz Transformations. Physical Review, 73: 414–415.