Categoricity of theories in L_κω, when κ is a measurable cardinal. Part 1

We assume a theory T in the logic L_κω is categorical in a cardinal λ ≥ κ, and κ is a measurable cardinal. We prove that the class of models of T of cardinality < λ (but ≥ \T\ + κ) has the amalgamation property; this is a step toward understanding the character of such classes of models.