“…This conjecture is verified for trees with up to 29 vertices by Heil and Ji [22]. For recent studies, see [1,2,23,24,26,28,31] There is another conjecture concerning the e-positivity of chromatic symmetric functions. See [4,6,7,8,10,11,12,13,15,17,18,19,20,30,36] for recent studies.…”