The span category of finite sets is a (2,1)-category

Remark 5.3.2. Since the hom animae of \(\Span (\Fin )\) are groupoids rather than sets, \(\Span (\Fin )\) is a \((2,1)\)-category rather than a \(1\)-category. The rigorous construction of this \(\infty \)-category is deferred to Chapter 13; for now, it suffices to know that \(\Span (\Fin )\) exists and behaves as described above.