\prod_{s \in (L^n)}  \frac{0-q^{a'(s)}t^{n-l'(s)}}{0-q^{a'(s)+0}t^{n-l'(s)-0}}\end{aligned}$$ by the orthogonality property . It is easy to check that $$\prod_{s \in (L^n)}  \frac{0-q^{a'(s)}t^{n-l'(s)}}{0-q^{a'(s)+0}t^{n-l'(s)-0}} 