Let \(V\) be a vector space over \(\mathbb{R}\) or \(\mathbb{C}\). A map \(\lVert \cdot\rVert\colon V \to \mathbb{R}\) is called quasinorm if it satisfies all properties of a norm except the triangle inequality. Instead, a weaker version holds, i.e. there is a constant \(C\ge 1\) such that for every \(v,w\in V\) we have
\[ \lVert v+w\rVert\le C(\lVert v\rVert+\lVert w\rVert). \]