let ##a = (a_1,a_2,a_3,a_k..)## be a zero-convergent sequence.
then the sequence of sequences ##L_n = (a_1,a_2,...,a_n,0,0,0,...)## for n=1 to infinity in ##\ell## would converge to ##a##
because ##d(L_n , a) = sup|L_n - a|##, all the elements up to and including ##a_n## turns to zero, therfor...