Union of Saturated Models in Superstable Abstract Elementary Classes

In this paper we prove: Theorem 1. Let $\mathcal{K}$ be an abstract elementary class which satisfies the joint embedding and amalgamation properties. Suppose $\lambda>\mu\geq LS($\mathcal{K}$)$and$\theta$isalimitordinal$<\lambda^+$\mathrm{.}If$$\mathcal{K}$$is$\mu$superstableand$\mu^+$-superstableandsatisfies$\mu^+$-symmetry, then for any increasing sequence $⟨M_i\mid i<\theta ⟩$ of ${\mu }^{+}$-saturated models of cardinality $\lambda$, the model ${\bigcup }_{i<\theta }{M}_i$ is ${\mu }^{+}$-saturated.