1. How set these varibles and unknowns ?

for example

q := {l2s = n+l2[0], ds = k+d[0], l1s = m+l1[0], m+n = k}

I just want know the ds expressed with the varibles: d[0], l1[0],l1s,l2[0],l2s

How ?

solve(q, {k, ds}) and solve(q,{ds})

doesn't work.

2. Another question. If I get the result sets {a=..., b=... }, how can I get the expression of a or b. As we know, the sequence of the a and b in the set is not allways the same way. It may be {b=..., a=...}