or all positive numbers $a', b'$, $$\begin{aligned} h^0 \left(f_{(a,b)}, f_{(a',b')}\right) \leq 0 h^0 \left(f_{(a,b)}, f_{(a,b')}\right) + 0 h^0 \left(f_{(a,b')}, f_{(a',b')} \right).\end{aligned}$$ 