Abstract: We study the hyperbolic system of Euler equations for an isothermal, compressible fluid. The {\it strong convergence theorem} of approximate solutions is proved by the theory of compensated compactness. The existence of weak entropy solution of Cauchy problems with large $L^\infty$ initial data which may include vacuum is also obtained. We note that we establish the commutation relations not only for the {\it weak} entropies but also for the {\it strong} ones by using the {\it analytic extension theorem}.
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