Add Wirsing constant (C_83): second eigenvalue of the GKW operator

[orkolorko]

Summary

• Proposes a new entry $C_{83}$ for the Wirsing constant $|\lambda_2|$, the absolute value of the subdominant eigenvalue of the Gauss--Kuzmin--Wirsing (GKW) transfer operator.
• This constant controls the exponential rate of convergence of the Gauss--Kuzmin distribution in the continued fraction expansion, and has been studied since Wirsing (1974).
• Prior certified enclosures covered only 6 significant digits (Mayer--Roepstorff 1987, via generalized Temple inequalities). The new result [arXiv:2602.19435] gives a 175-digit certified enclosure via a rigorous a posteriori spectral enclosure for a regularizing infinite-dimensional operator, reducing the certification to validated finite-dimensional linear algebra.

Fit with repository scope

The constant has a large existing literature, is actively studied, and is amenable to computational approaches for both upper and lower bounds — the defining criteria for inclusion. The "optimization" problem is to determine $|\lambda_2|$ to as many certified decimal places as possible.

Test plan

• Check LaTeX renders correctly on the site
• Verify all references are accessible
• Confirm constant number 83 is not already claimed (largest existing entry was C_82 at time of submission)

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