This contribution is devoted to the study of positional numeration systems with negative base introduced by Ito and Sadahiro in 2009, called (-beta)-expansions. We give an admissibility criterion for more general case of (-beta)-expansions and discuss the properties of the set of (-beta)-integers. We give a description of distances within this set and show that this set can be coded by an infinite word over an infinite alphabet, which is a fixed point of a non-erasing non-trivial morphism.
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