  A new perturbational approach to spectral and thermal properties of strongly
correlated electron systems is presented: The Anderson model is reexamined for
$U\to\infty$\,, and it is shown that an expansion of Green's functions with
respect to the hybridization $V$ built on Feynman diagrams obeying standard
rules is possible. The local correlations of the unperturbed system (the atomic
limit) are included exactly through a two-particle vertex. No auxiliary
particles are introduced into the theory. As an example and test the small
energy scale and many-body resonance of the Kondo problem are reproduced
analytically.
