Svarc-Milnor Lemma: a proof by definition

Abstract

The famous Švarc-Milnor Lemma says that a group $G$ acting properly and cocompactly via isometries on a length space $X$ is finitely generated and induces a quasi-isometry equivalence $g\to g\cdot x_0$ for any $x_0\in X$. We redefine the concept of coarseness so that the proof of the Lemma is automatic.