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Let all rational numbers qn of the real axis be covered by intervals In of measure |In|=2n, such that qn is the centre of In. Then the endpoints are rational numbers. The irrational numbers x of the complement of infinite measure, not covered by the intervals In, form particles of a totally disconnected space, so-called "Cantor dust" Ξ.

Every particle xΞ must be separated from every particle yΞ by at least one rational number qn and hence by at least one interval In covering qn. Since the end points of the In are rational numbers too, also being covered by their own intervals, the particles of Cantor dust can only be limits of infinite sequences of overlapping intervals In.

If intervals don't overlap, then they cannot form a common limit; their limits must lie between them. But in any case infinitely many finite intervals are required to establish one limit. And in any case two limits must be separated by infinitely many overlapping intervals

Such an infinite set of overlapping intervals is called a cluster. In principle, given a fixed and complete enumeration of the rationals, we can calculate every cluster and the limits of its union. Therefore, every irrational xΞ can be put in bijection with the pair of clusters, i.e., the infinite set of intervals converging to it. There are countably many sets In and therefore not more than countably many disjoint clusters with limits and therefore not more limits.

Where are the other irrational numbers of the complement?

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