i have a function f:A->B, im also given that |B|<=null aleph, and for every b in B, |f^-1({b})|<=null aleph, i need to prove that |A|<=null aleph.(adsbygoogle = window.adsbygoogle || []).push({});

basically i think that A equals the union of f^-1({b}) for every b in B, and by another theorem i can consequently assert that |A|<=null aleph.

but is this correct?

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# Aleph null problem.

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