  Let G be a reductive group over a non-Archimedean local field. Then the
canonical functor from the derived category of smooth tempered representations
of G to the derived category of all smooth representations of G is fully
faithful. Here we consider representations on bornological vector spaces. As a
consequence, if V and W are two tempered irreducible representations and if V
or W is square-integrable, then Ext_G^n(V,W) vanishes for all n>0. We use this
to prove in full generality a formula for the formal dimension of
square-integrable representations due to Schneider and Stuhler.
