  Let $G$ be a simply-connected simple compact Lie group and let $M$ be an
orientable smooth closed 4-manifold. In this paper we calculate the homotopy
type of the suspension of $M$ and the homotopy types of the gauge groups of
principal $G$-bundles over $M$ when $\pi_1(M)$ is: (1)~$\mathbb{Z}^{*m}$,
(2)~$\mathbb{Z}/p^r\mathbb{Z}$, or
(3)~$\mathbb{Z}^{*m}*(*^n_{j=1}\mathbb{Z}/p_j^{r_j}\mathbb{Z})$, where $p$ and
the $p_j$'s are odd primes.

Algebraic Topology