  Given a sequence of points in the unit disk, a well known result due to
Carleson states that if given any point of the sequence it is possible to
interpolate the value one in that point and zero in all the other points of the
sequence, with uniform control of the norm in the Hardy space of bounded
analytic functions on the disk, then the sequence is an interpolating sequence
(i.e.\ every bounded sequence of values can be interpolated by functions in the
Hardy space). It turns out that such a result holds in other spaces. In this
short note we would like to show that for a given sequence it is sufficient to
find just {\bf one} function interpolating suitably zeros and ones to deduce
interpolation in the Hardy space.
