It is a standard fact that if $X$ is a path-connected CW-complex, then:
$$[X,K(G,n)] = H^n(X;G)$$
where:
$G$ is an abelian group;
$n>1$ is an integer;
$K(G,n)$ is the Eilenberg-Maclane space;
$[X,K(G,n)]$ is the set of homotopy classes of maps $X \to K(G,n)$;
$H^n(X;G)$ is the $n$th singular co...
In mathematics, tetration (or hyper-4) is iterated, or repeated, exponentiation. It is the next hyperoperation after exponentiation, but before pentation. The word was coined by Reuben Louis Goodstein from tetra- (four) and iteration. Tetration is used for the notation of very large numbers. The notation
n
a
{\displaystyle {^{n}a}}
means
a
a...
