  Tang et al. [Science 361, 570 (2018)] report on the properties of Dirac
fermions with both on-site and Coulomb interactions. The substantial decrease
up to ~40% of the Fermi velocity of Dirac fermions with on-site interaction is
inconsistent with the numerical data near the Gross-Neveu quantum critical
point. This results from an inappropriate finite-size extrapolation.
