  The interpolating sequences for $H^{\infty}({\mathbb{D}}),$ the bounded
holomorphic function in the unit disc ${\mathbb{D}}$ of the complex plane
${\mathbb{C}},$ {\small where characterised by L. Carleson by metric conditions
on the points. They are also characterised by "dual boundedness" conditions
which imply an infinity of functions. A. Hartmann proved recently that just one
function in $H^{\infty}({\mathbb{D}})$ was enough to characterize interpolating
sequences for $H^{\infty}({\mathbb{D}}).$ In this work we use the "hard" part
of the proof of Carleson for the Corona theorem, to extend Hartman's result and
answer a question he asked in his paper.}\ \par
