function res = hlp12(t,y)

a = -0.5;   %  x(0) = -0.5
b = 1;      %  y(0) = 1

%  dx = y + x*y^2
%  dy = x - y + y^3
res = [y(2) + y(1)*y(2)*y(2);y(1) - y(2) + y(2)^3];