Representability of cohomology by Eilenberg–MacLane spaces ($[X,K(G,n)]\cong H^n(X;G)$)

For a CW complex $X$, abelian $G$ and $n\ge 1$, homotopy classes of maps to the Eilenberg–MacLane space correspond to cohomology classes by pullback of the universal cohomology class of an Eilenberg–MacLane space. Pointed maps give the reduced version. This converts a cohomology class into an actual map realizing its effect on homotopy.