T-structure criterion for CN-realizable matrices

Let MM be a strictly upper triangular (0,2)(0,2)-matrix, meaning that its entries are 00 or 22, and suppose that for each k3k\geq 3 there is at most one pair (i,j)(i,j) with ji=kj-i=k and M(i,j)=2M(i,j)=2. A graph on the grid alignment G(M)G(M) has a T-structure when it satisfies conditions (C1), (C2), and (C3) specified in the source: path lengths satisfy (C1), and the edge configurations satisfy (C2) and (C3). The matrix MM is CN-realizable when it is the CN matrix of a pure braid projection. T-structure conjecture. If MM has a T-structure, then MM is CN-realizable. The source notes that some CN-realizable matrices have no T-structure, so the proposed condition is sufficient rather than necessary; its general status is not resolved.

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Primary source

Yuko Ozawa, Ayaka Shimizu and Yoshiro Yaguchi, “The CN matrix of a pure braid projection”, arXiv:2506.08659 (2025).

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