function err = KB4s(x)
%

F(1) = -0.7+x(1);
F(2) = -0.5+(1-x(1))+x(2)-(1-x(1))*x(2);
F(3) = -0.5+(1-x(2))+x(3)-(1-x(2))*x(3);
err = norm(F);
