var
   x  {1..4} >= -10, <= 10;
subject to
cons1:       x[1] + x[2] + x[3] + x[4] = 1;
cons2:       x[1] + x[2] - x[3] + x[4] = 3;
cons3:       x[1]^2 + x[2]^2 + x[3]^2 + x[4]^2 = 4;
cons4:       x[1]^2 + x[2]^2 + x[3]^2 + x[4]^2 - 2 * x[1] = 3;


solve;
display x;