# LIB2-061 — The reactor-angle formula retains an unforced round-trip readout

- class: CLAIM · review_state: PUBLISHED · house_tier: not yet assigned
- labels as printed: math_status Structural · attachment NOT_PRINTED · scorecard tier word Structural (PDF p.58)
- basis: {"pdf_sha256_prefix": "b64ddcd9e16a6dcd", "release": "Rev33.1_S369"}

## Statement

The retained reactor-angle formula is sin²θ13 = sin⁴(π/8); its round-trip T² squaring (the round-trip framing, exponent 2) is identified but not forced from first principles.

## Caution

Identifying the round-trip construction does not select its physical readout or promote the formula to a theorem.

## Primary source

Paper 5, §2, Reactor-angle expression, PDF p.83: "sin2 θ13 = sin4 (π/8)"

## Machine

- url: /library-v2/LIB2-061/
- content_sha256: c250d9bd0df5977478f385144a46dae325cedf2682ca3660022890eedc7cf3fc
- candidate_ids: C2-006 C2-060

## Freshness

- BUILD_STAMP S371a · 2026-09-26T22:53Z · master 01d1a5873ede42f5 · cut 9dcc6ce9a8ee3e02
- Declared volatile fields (R36): BUILD_STAMP