ll apply the preceding discussion
| to vector bundles in the next chapter, and
| the following local criterion will be useful.
|
| Proposition 2.7.  Let f : X -&gt; Z be a morphism,
|
|                   and g : Z x W -&gt; Z be the
|
|                   projection on the first factor.
|
|                   Then f, g have a fiber product,
|
|                   namely the product X x W
|
|                   together with the morphisms
|
|                   of the following diagram:
|
|                 f x id