A remark on the counterexample to the unknotting number conjecture

By using Snappy, M. Brittenham and S. Hermiller discovered a very surprising example that $u(7_1\mathrm{\#}\overline{7_1})\le 5<6=u(7_1)+u(\overline{7_1})$, where $7_1$ is the $(2,7)$-torus knot and $\overline{7_1}$ is its mirror image. Based on their work, we give a direct verification of this fact.