 we have the following lemma:  \[lem-def0a\] Suppose that $h:B'\rightarrow B$ is type (IIIa). Then we have exact sequences: $$\begin{aligned} 0 \rightarrow {\mathbb{E}\text{xt}_{{\mathcal O}_{B'}}}^0(L_{\zeta'},{\mathcal O}_{B'}) \rightarrow {\mathbb{E}\text{xt}_{{\mathcal O}_{B}}}^0(L_\zeta,{\mathcal O}_B) \rightarrow 