  We consider the classical problem of the construction of invariant tori
exploiting suitable Hamiltonian normal forms. This kind of approach can be
translated by means of the Lie series method into explicit computational
algorithms, which are particularly suitable for applications in the field of
Celestial Mechanics. First, the algorithm constructing the Kolmogorov normal
form is described in detail. Then, the extension to lower-dimensional elliptic
tori is provided. We adopt the same formalism and notations in both cases, with
the aim of making the latter easier to understand. Finally, they are both used
in a combined way in order to approximate carefully the secular dynamics of the
extrasolar system hosting two planets orbiting around the HD 4732 star.
