The first-increase inequalities for connected unit interval graphs

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Let GG) be a connected unit interval graph defined by the weakly increasing sequence m=(m1,m2,…,mn−1){\bf m}=(m_1,m_2,\ldots,m_{n-1}), where i≤mi≤ni\leq m_i\leq n for all i∈[n−1]i\in[n-1]. Let mr<mr+1m_r<m_{r+1} be the first increase, and let G′G' be the unit interval graph defined by

m′=(m1+1,…,mr+1,mr+1,…,mn−1).{\bf m}'=(m_1+1,\ldots,m_r+1,m_{r+1},\ldots,m_{n-1}).

First-increase inequalities. One has

G≥eG′andG≥sG′.G\geq_e G'\qquad\text{and}\qquad G\geq_s G'.

These inequalities are proposed as part of a sequence of comparisons between connected unit interval graphs that could establish their ee-positivity and Schur-positivity. The Schur-positivity consequence is already known for unit interval graphs, while the corresponding ee-positivity goal remains open in the stated context.

References

Primary source

Samantha Dahlberg, Adrian She and Stephanie van Willigenburg, “Chromatic Posets”, arXiv:1909.12394 (2020).

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