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Show that the set is infinite by placing it in a one to one correspondence with a proper subset of it self. Give the general term of the original set, and show its pairing with its proper subset {15,17,19,21,23,...}
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This one-to-one correspondence is n <---> n+2.
The set of all odd whole numbers starting from 15 then one-to-one corresponds to its proper subset
of all odd whole numbers starting from 17.