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We extend the reduction method of JuzvinskiÄ to non compact dynamics. We show that the method could be used to prove results on entropies of transformations on non compact metric or Polish spaces. This is illustrated in three situations. First we extend the results of P. Walters on transformations with complete positive entropy. Then we extend the Abramov-Rohlin addition formula of R. K. Thomas. Finally we use the addition formula to extend the results of Walters on the uniqueness of invariant measures with maximal entropy.
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