 Eilenberg–MacLane space

A connected Eilenberg–MacLane space $K(G,n)$, $n\ge 1$, has ${\pi }_n\cong G$ and all other positive-degree homotopy groups trivial. The group $G$ must be abelian when $n\ge 2$, but may be nonabelian when $n=1$. For an abelian group, the Dold–Kan correspondence constructs a simplicial model from the chain complex concentrated in degree $n$. A classifying space of a discrete group gives the general $K(G,1)$ case.

An Eilenberg-MacLane space is a fundamental concept in algebraic topology, named after mathematicians Samuel Eilenberg and Saunders Mac Lane. It is used to study topological properties related to cohomology theories and homotopy theory.