Generalized Kruskal conjecture for product-vector sums

Let n2n\geq 2, m1m\geq 1, and d1,,dm1d_1,\dots,d_m\geq 1 be integers. Let X1,,Xm\mathcal{X}_1,\dots,\mathcal{X}_m be vector spaces over a field F\mathbb{F}, and let

{xa=xa,1xa,m:a{1,,n}}X1Xm\{x_a=x_{a,1}\otimes\dots\otimes x_{a,m}:a\in\{1,\dots,n\}\}\subset \mathcal{X}_1\otimes\dots\otimes\mathcal{X}_m

be non-zero product vectors such that, for each j{1,,m}j\in\{1,\dots,m\},

dimspan{xa,j:a{1,,n}}dj.\dim\operatorname{span}\{x_{a,j}:a\in\{1,\dots,n\}\}\geq d_j.

If n1j=1m(dj1)n-1\leq\sum_{j=1}^m(d_j-1) and

a=1nxa=0,\sum_{a=1}^n x_a=0,

then there exists a non-empty strict subset Γ{1,,n}\Gamma\subset\{1,\dots,n\} such that

aΓxa=0.\sum_{a\in\Gamma}x_a=0.

Generalized Kruskal conjecture. Under these hypotheses, a nontrivial zero-sum subcollection must exist. This relaxes general position to lower bounds on the dimensions of the subsystem spans and replaces pairwise cancellation by cancellation of an arbitrary non-empty strict subcollection. The stated consequence was previously proved, so this conjectural formulation is solved.

Sources & referencesView supporting material

Primary source

Benjamin Lovitz, “Toward a generalization of Kruskal's theorem on tensor decomposition”, arXiv:1812.00264 (2020).

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