Remark 11.4.0.2. The formation of Eilenberg-MacLane spaces $A \mapsto \mathrm{K}(A,n)$ is defined for every integer $n$. However, it is only interesting for $n \geq 0$: if $n$ is negative, then the simplicial abelian group $\mathrm{K}(A,n)$ is trivial (that is, it is isomorphic to $\Delta ^0$ as a simplicial set).
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$