variables
  x[4] in (0; 0; 0; 0);

function f(x[4])
  return(x(1)*(-1 + x(1)*x(2)*x(3)*x(4)); x(2)*(-1 + x(1)*x(2)*x(3)*x(4)); x(3)*(-1 + x(1)*x(2)*x(3)*x(4)); x(4)*(-1 + x(1)*x(2)*x(3)*x(4)));
end

function v(u[4])
  return(u(1)^2 + u(2)^2 + u(3)^2 + u(4)^2);
end