i was lazy to upload image :) both solutions are correct, it depends on conditions :P for a^mn
> solve(m^2-m*(m-n));
print(`output redirected...`); # input placeholder
{m = 0, n = n}, {m = m, n = 0}
> solve(m^2-m*(m-n));
print(`output redirected...`); # input placeholder
{m = 0, n = n}, {m = m, n = 0}