Let {q_{n}} be an enumeration of the rationals, and for each n, let U_{n} be an open interval of length 1/2^{n} centered at q_{n}. Denote the union of all U_{n} by U. Then U is a dense open . . . [Read More]


Let {q_{n}} be an enumeration of the rationals, and for each n, let U_{n} be an open interval of length 1/2^{n} centered at q_{n}. Denote the union of all U_{n} by U. Then U is a dense open . . . [Read More] 

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