Pairwise structure conjecture for equal smallest minors

Let I,J([n]k)I,J\in\binom{[n]}{k}, let r=IJ=JIr=|I\setminus J|=|J\setminus I|, and form the lattice path P(I,J)P(I,J) from the ordered symmetric difference, with an up step for an element of IJI\setminus J and a down step for an element of JIJ\setminus I. Assume P(I,J)P(I,J) is a Dyck path. A pair is pp-interlaced when the path has pp peaks, and in the 2-interlaced case write its successive up- and down-run lengths as (α1,β1,α2,β2)(\alpha_1,\beta_1,\alpha_2,\beta_2).

Pairwise smallest-minors conjecture. There exists an arrangement of smallest minors S([n]k)S\subset\binom{[n]}{k} containing II and JJ if and only if either the pair is 1-interlaced, equivalently weakly separated, or it is 2-interlaced and

αiβj\alpha_i\ne\beta_j

for every ii and jj.

This conjecture describes which pairs can occur together among equal minimal Plücker coordinates. The paper studies the conjecture through plabic graphs and proves related cases and constructions, but the supplied text gives no resolution of this exact statement.

Sources & referencesView supporting material

Primary source

Miriam Farber and Alexander Postnikov, “Arrangements of equal minors in the positive Grassmannian”, arXiv:1502.01434 (2015).

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