Chromatic quasisymmetric function evaluated at q=-1

Shareshian and Wachs have shown that the chromatic
quasisymmetric function of the natural unit interval graph is
symmetric (Shareshian--Wachs, 2016). In this talk, we prove that the
chromatic quasisymmetric function of any unit interval graph is
symmetric at  q=-1, and present a combinatorial interpretation of it
in the Schur expansion.