 aim at finding a rectangle $\mathcal{R}$ containing $(a,b)$ such that $${\mathcal{C}}\cap \mathcal{R} \subset \left\{(a',b') \in   (0,+\infty)^0, \, h^0 (f_{(a,b)}, f_{(a',b')}) \leq \xi \right\}.$$ For 