Ok, Thanks.
I got the first two questions and the first part of question 3.
But the second part of 3 has still got me confused - since the number of elements in a different
than 0 are finite , the sum of $\left\lVert{a}\right\rVert\infty$ over a=(1,1,1,1,...0,0,0) will not
be $\infty$ but a...