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F. Trèves, in [T2], applied the Concatenation Method and Carleman's Method to show uniqueness in the Cauchy problem, for certain degenerate hyperbolic equations, depends on the lower order terms. Lu, A., Mai, M. and Wang, G. in [LMW], used an Energy Estimate to study the existence of solutions of the Cauchy problem for the same operator class as [T2]. In this work, we stdy in detail the paper [T2] and Theorem 1 of [TMW].