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2407.20890

Shift operators and their classification

Maria Carvalho, Udayan B. Darji, Paulo Varandas

correctmedium confidence
Category
Not specified
Journal tier
Specialist/Solid
Processed
Sep 28, 2025, 12:56 AM

Audit review

The paper’s Theorem 2.10 states and proves that, on a finite-dimensional Banach space X with a basis E having S-bounded projections, the shift σ_S on ℓ^p(X) is conjugate to a finite product of bilateral weighted backward shifts. The proof constructs coordinate maps Γ_b, assembles them into an isomorphism I: ℓ^p(X) → (ℓ^p(K))^{dim X}, and shows I ∘ σ_S = (∏_{x∈E} B_{ω(x)}) ∘ I, using the identity S_{n+1}(e_{n+1}(x)) = ω_{n+1}(x) e_n(x) and the S-bounded projections hypothesis to guarantee boundedness and surjectivity of the coordinate maps . The candidate solution reproduces the same strategy (coordinate extraction along the moving normalized bases and synthesis), differing only in notation (coordinate functionals φ_{n,x} vs. projections Π_{e_n(x)}) and in showing the inverse explicitly rather than appealing to the open mapping theorem. No substantive gaps or contradictions were found.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} specialist/solid

\textbf{Justification:}

The classification result is correct and methodologically sound. The argument cleanly reduces the dynamics of σ\_S to a block-diagonal product of weighted backward shifts, enabling transfer of dynamical properties. Minor editorial improvements (assumption placement, unification of norm estimates across p, and a brief equivalence note between projections and coordinate functionals) would further enhance clarity.