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4 papers
A planar network proof for Hankel total positivity of type Narayana polynomials
Ethan Y. H. Li, Grace M. X. Li, Arthur L. B. Yang +1
The Hankel matrix of type B Narayana polynomials was proved to be totally positive by Wang and Zhu, and independently by Sokal. Pan and Zeng raised the problem of giving a planar n…
Immanant Positivity for Catalan-Stieltjes Matrices
Ethan Y. H. Li, Grace M. X. Li, Arthur L. B. Yang +1
In this paper we give some sufficient conditions for the nonnegativity of immanants of square submatrices of Catalan-Stieltjes matrices and their corresponding Hankel matrices. To…
The twinning operation on graphs does not always preserve -positivity
Ethan Y. H. Li, Grace M. X. Li, David G. L. Wang +1
Motivated by Stanley's -free conjecture on chromatic symmetric functions, Foley, Hoàng and Merkel introduced the concept of strong -positivity and conjectured th…
The -positivity of two families of -free graphs
Grace M. X. Li, Arthur L. B. Yang
Motivated by Stanley's conjecture about the -positivity of claw-free incomparability graphs, Hamel and her collaborators studied the -positivity of -free graphs, w…