Schiffler Problem 6.3
Schiffler Problem 6.3
For admissible parameters and any two lattice paths , does equality of their Lagrange numbers imply that their associated band graphs are isomorphic? That is, is sufficient to conclude ? This is false: there exist such that but .
Progress summary
A new preprint gives a counterexample, showing that the proposed uniqueness claim is false.
Schiffler Problem asks whether equal Lagrange numbers force band graphs to be isomorphic. A new explicit counterexample answers this question negatively.
August 2026 counterexample
The preprint constructs the counterexample in the class , proving that equal Lagrange numbers do not determine the band graph up to isomorphism.
Current status (as of August 2026): Schiffler Problem is resolved negatively by an explicit counterexample; related classification questions remain open.
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