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Existence of epichristoffel words of arbitrary lengths for fixed k-letter alphabets

Determine whether, for every fixed integer k ≥ 3 and every positive integer n, there exists an epichristoffel word of length n over a k-letter alphabet.

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Background

Paquin provided an algorithm (via the operator T) to decide existence of epichristoffel k-tuples (letter counts), but a general length-existence theorem across all alphabets of size k ≥ 3 was left open. This paper introduces epichristoffel trees and corresponding Stern–Brocot constructions to generate infinite families of lengths and proves specific existence results for k=3 (e.g., Theorem 5.3). Nonetheless, the fully general claim—existence for every length n and each fixed k ≥ 3—remains unresolved.

References

Although epichristoffel words share many of the same properties as Christoffel words, Genevieve raised some open problems regarding epichristoffel words. These include the ability to characterize the epichristoffel word of each conjugacy class, whether epichristoffel words satisfy a type of balanced property, and whether there is an epichristoffel word of any length over a k-letter alphabet for a fixed k ≥ 3.

On a Generalization of the Christoffel Tree: Epichristoffel Trees (2507.15313 - Krishnamoorthy et al., 21 Jul 2025) in Section 1. Introduction