5 problems

Zhang and Zhang's conjecture. The polynomial

Li et al.'s conjecture. The polynomial $\zeta(H,x)$ is log-concave.

Let $H$ be a hexagonal system, and let its Clar covering polynomial be … where $c(H,k)$ is the number of Clar covers of $H$ having precisely $k$ hexagons. Log-concavity conjecture…

Let $H$ be a hexagonal system, and let its Clar covering polynomial be … where $c(H,k)$ is the number of Clar covers of $H$ having precisely $k$ hexagons. Zhang–Zhang's unimodality…

Let $H$ be a hexagonal system, and let its sextet polynomial be the polynomial whose coefficients count sextet-related structures of $H$. Log-concavity conjecture for sextet polyno…