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Weakly-wandering set

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for an invertible measurable transformation of a measurable space

A measurable subset for which there is an infinite sequence of integers such that the sets are mutually disjoint (here, invertibility of is understood to mean existence and measurability of ). If has a -finite quasi-invariant measure (defined on ), then a necessary and sufficient condition for to have a finite invariant measure equivalent to is that for any weakly-wandering set .

A word of warning. In topological dynamics there is a notion of weakly non-wandering point (see [3]) which has nothing to do with the notion defined above.

References

[1] A.B. Hajian, S. Kakutani, "Weakly wandering sets and invariant measures" Trans. Amer. Math. Soc. , 110 : 1 (1964) pp. 136–151
[2] A. Hajian, Y. Itô, "Weakly wandering sets and invariant measures for a group of transformations" J. Math. Mech. , 18 : 12 (1969) pp. 1203–1216
[3] D.V. Anosov, I.V. Bronshtein, "Topological dynamics" , Dynamical Systems I , Encycl. Math. Sci. , I , Springer (1988) pp. 197–219 (Translated from Russian)
How to Cite This Entry:
Weakly-wandering set. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Weakly-wandering_set&oldid=33108
This article was adapted from an original article by D.V. Anosov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article