  This article gives an elementary computational proof of the group law for
Edwards elliptic curves. The associative law is expressed as a polynomial
identity over the integers that is directly checked by polynomial division.
Unlike other proofs, no preliminaries such as intersection numbers, Bezout's
theorem, projective geometry, divisors, or Riemann Roch are required. The proof
of the group law has been formalized in the Isabelle/HOL proof assistant.
