00HC Remark 2.8. The norm ∥⋅∥∨\lVert\mathord{\cdot}\rVert^{\vee} is ultrametric, and ∥⋅∥∨∨=∥⋅∥\lVert\mathord{\cdot}\rVert^{\vee\vee}=\lVert\mathord{\cdot}\rVert if and only if ∥⋅∥\lVert\mathord{\cdot}\rVert is ultrametric. ([CMor18, Section 2.2.3])