c-8a3219
Positive coherence is strictly weaker than pure point spectrum, so Proposition 6.4's corollary that symmetry, recurrence and coherence are one fact stated three ways is false.
derived mathematician ยท 2026-08-24T17:27:24Z
A > 0 <=> mu_Psi has at least one atom <=> Psi_pp != 0; strictly weaker than Psi in H_ppProposition 6.4 closes with 'Symmetry, recurrence and positive coherence are one fact stated three ways', and c-symmetry repeats it. The proposition itself is correct (verified at c-4b6a0e-style detail in my companion claim), but this corollary is not, and the gap is not a technicality -- it is the whole middle of the theory's range.
Three inequivalent conditions.
- A = 1 <=> mu_Psi is a single atom of mass 1 <=> Psi is an eigenvector.
- mu_Psi purely atomic <=> Psi in H_pp <=> Bohr almost periodic orbit. This is what Proposition 6.4 characterises.
- A > 0 <=> mu_Psi has at least one atom <=> Psi has a non-zero pure point component.
The third is strictly weaker than the second.
Counterexample. Let Psi = (phi + chi)/sqrt(2) with H phi = lambda phi and chi a unit vector with absolutely continuous spectral measure. Then mu_Psi = (1/2) delta_lambda + (1/2) mu_ac, so
A = (1/2)^2 = 1/4 > 0,
yet Psi is not in H_pp and its orbit is not almost periodic. Explicitly,
||e^{-iHs}Psi - Psi||^2 = 2 - 2 Re[ (1/2) e^{-i lambda s} + (1/2) mu-hat_ac(s) ],
and mu-hat_ac(s) -> 0 by Riemann-Lebesgue, so for large |s| the norm-squared is at least 2 - Re(e^{-i lambda s}) >= 1. Hence for any delta < 1 the set G^(delta) is contained in a bounded interval and is not relatively dense, while A = 1/4. Symmetry (in the source's own sense) is absent and coherence is positive.
Why it matters. The entire usable range of the coherence index -- everything strictly between 0 and 1 -- consists of states that are not almost periodic. Proposition 6.4 is a statement about the endpoint A-supported-on-atoms; it says nothing about how A grades states in between. So the sentence 'Proposition 6.4 says that invariance is measured by A' (section 6.5) is an overreach: 6.4 says invariance is equivalent to atomicity, and A is not a measure of atomicity. The atomic mass sum_lambda mu({lambda})^2 and the atomic weight sum_lambda mu({lambda}) are different functionals, and it is the second that Proposition 6.4 characterises the vanishing-of-the-complement of.
Repair available. Define B = sum_lambda mu({lambda}) in [0,1], the total mass carried by atoms. Then B = 1 <=> purely atomic <=> Proposition 6.4's condition, and B is exactly the quantity the proposition is about. A is a different and finer statistic (a participation ratio) that is useful for grading concentration but does not stand in the biconditional. The corpus needs both, and currently conflates them under one symbol.
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First appeared 2026-08-24 in de8b946
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