The majorization characterization conjecture for ordinal spaces embeddable in the line

Let (X,δ)(X,\delta) be an ordinal space with X=nN+|X|=n\in\mathbb N^+, and let x1,x2,,xnx_1,x_2,\ldots,x_n be an enumeration of its points satisfying the majorization property. Write XR1X\hookrightarrow\mathbb R^1 for embeddability of XX in the real line. Majorization characterization conjecture. If such an enumeration exists, then

XR1.X\hookrightarrow\mathbb R^1.

The paper proves that line embeddability implies the existence of an enumeration with the majorization property and states sufficiency for n4n\leqslant4, while explicitly saying that it cannot determine whether sufficiency holds for n>5n>5; the general assertion is therefore open.

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Primary source

Karsten Keller and Evgeniy Petrov, “Ordinal spaces”, arXiv:2412.17391 (2024).

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