First Chern class of a tensor product of complex line bundles
= First Chern class of a tensor product of complex line bundles
{title2=$c_1(L\otimes M)=c_1(L)+c_1(M)$}
The <First Chern class> turns the <tensor product of vector bundles> of <complex line bundles> into addition in integral <cohomology>. This follows by computing the universal <complex line bundle> on the product of two <Complex projective spaces> and restricting to each factor. The proof retains <torsion elements>, which differential forms alone cannot detect.