A note on almost negative matrices and Gromov-hyperbolic Coxeter groups

We revisit Moussong’s characterization of Gromov-hyperbolic Coxeter groups. Moussong showed that a Coxeter group is Gromov-hyperbolic if and only if it does not contain a subgroup isomorphic to $\mathbb Z^2$. This property can be read off directly from the defining graph. We show that there is a gap in the original argument and provide a workaround.