intror2:= function(n)
local r, x, i;
x:= [];
i:= 1;
Print("The solutions to x^2 = -1 in Z_", n, " are ");
r:= Elements(Integers mod n);
  repeat
    if Int(r[i]^2) = n-1 then
    Add(x,r[i]);
    fi;
    i:= i+1;
  until i=n+1;
return x;
end;