function err = KB3is(x)
%

F(1) = -0.55+x(1)+x(2)+x(5)-x(1)*x(2)-x(1)*x(5)-x(2)*x(5)+x(1)*x(2)*x(5);
F(2) = -0.55+x(3)+x(4)+(1-x(5))-x(3)*x(4)-x(3)*(1-x(5))-x(4)*(1-x(5))+x(3)*x(4)*(1-x(5));
err = norm(F);
