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

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

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

constraints
  x(1)<=x(2);
  x(1)<=x(3);
  x(1)<=x(4);
end