  Given a finite set \sigma of the unit disc \mathbb{D}={z\in\mathbb{C}:,
|z|<1} and a holomorphic function f in \mathbb{D} which belongs to a class X,
we are looking for a function g in another class Y (smaller than X) which
minimizes the norm |g|_{Y} among all functions g such that
g_{|\sigma}=f_{|\sigma}.
