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In topology, a topological space is said to be resolvable if it is expressible as the union of two disjoint dense subsets. For instance, the real numbers form a resolvable topological space because the rationals and irrationals are disjoint dense subsets. A topological space that is not resolvable is termed irresolvable.
Properties

The product of two resolvable spaces is resolvable
Every locally compact topological space without isolated points is resolvable
Every submaximal space is irresolvable

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Resolvable space