124 citations · 735 across the 42 of their papers we have counts for
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math.CO2004
Counterexamples to the Neggers-Stanley conjecture
Petter Brändén
The Neggers-Stanley conjecture (also known as the Poset conjecture) asserts that the polynomial counting the linear extensions of a partially ordered set on by thei…
math.CO2004
Sign-graded posets, unimodality of -polynomials and the Charney-Davis Conjecture
Petter Branden
We generalize the notion of graded posets to what we call sign-graded (labeled) posets. We prove that the -polynomial of a sign-graded poset is symmetric and unimodal. This exte…
math.CO2004★ 24 cited
On linear transformations preserving the Pólya Frequency property
Petter Brändén
We prove that certain linear operators preserve the Pólya frequency property and real-rootedness, and apply our results to settle some conjectures and open problems in combinatoric…