## how to prove \int_{M} u \wedge f^{*} v = \int_{N} w \wedge v if f is a submersion?

M,N are smooth manifolds. dim M=m,dim N=n.f:M---->N is a submersion.
Let u is a r-form on M, v is a (m-r)-form on N.
Please prove that there exists a (r-m+n)-form w on N such that
\int_{M} u \wedge f^{*} v = \int_{N} w \wedge v.
Please tell me in detail.thanks very much!