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Ramanujan-Petersson: rename to Ramanujan & update informal proof - #669

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@seewoo5 seewoo5 commented Nov 6, 2026

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Following the Zulip discussion #Sphere packing in 8 dimensions > SphereCeti @ 💬

The conjecture for $\tau(p)$ is due to Ramanujan, where Ramanujan-Petersson refers to the general statement on cuspidal Hecke eigenforms. But it seems that the id is frozen so I only change the docstring. Also, informal proofs are corrected, following the above Zulip discussion.

This was (again) written by Claude, so it would be great if someone can take a look.

… proof

Following the Zulip discussion (Sphere packing in 8 dimensions > SphereCeti):

- The bound |τ(p)| ≤ 2 p^(11/2) is Ramanujan's conjecture alone; the
  Ramanujan–Petersson conjecture is Petersson's generalisation to all
  cuspidal eigenforms. Retitle the problem and update the notes and Lean
  docstrings accordingly, and drop Petersson's paper from the sources.
- The informal proof wrongly located τ(p) in the étale cohomology of the
  universal elliptic curve. Weight-12 eigenvalues live in H¹_! of the
  modular curve with coefficients in Sym¹⁰ R¹f_*Q_ℓ, and through it in
  H¹¹ of the 10-fold fibre power (Kuga–Sato variety). Rewrite the sketch:
  Eichler–Shimura isomorphism and congruence relation give
  X² − τ(p)X + p¹¹, and purity comes either from Weil I applied to a
  smooth compactification of the Kuga–Sato variety (Deligne 1969/1974)
  or from Weil II applied to the sheaf directly (Freitag–Kiehl). Add the
  Weil II and Freitag–Kiehl references.

The problem ID and the theorem name stay `ramanujan_petersson`: the ID
is a member of the frozen v1 set, and renaming the theorem would change
the trusted statement and require a statement revision. The Lean
statement itself is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SXjhFkcnZG1eciaA1Rjhdh
@seewoo5

seewoo5 commented Nov 6, 2026

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@alreadydone Could you review this one?

Co-authored-by: Junyan Xu <junyanxu.math@gmail.com>
Co-authored-by: Junyan Xu <junyanxu.math@gmail.com>
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