In $\textit{Atiyah and Bott: The Yang-Mills equations over riemann surfaces}$, there is a sentence about the topology of BU(n) (i.e. the classifying space of U(n)):
Here $K(\mathbb{Z},n)$ means the Eilenberg-MacLane space with the $n^{th}$ homotopy group $\mathbb{Z}$. Does anybody know what's the meaning of the symbol ${\simeq \atop \mathbb{Q}}$? Does anyone know a reference (or a proof) for the statement? Thanks a lot!